1. Chemistry

IF 80mg of a radioactive element decays to 10mg in 30 minutes, the half-life of this element is a.10 min b.20 min c.30 min d.40 min the answer is a.10 min but i would like to know why, please help.

2. physics

a car, moving at 100 mi/hr, passes a stationary police car whose siren has a frequency of 500 Hz. what is the frequency change heard by observer in the moving car as he passes the police car? the velocity of sound in air is 343 m/s. ( 1 mi= 1.609 km).

3. Math

A box has a volume of 7500 cm3 and a surface area of 2600 cm2. What are length, width, and height of the box?

4. Chemistry

Phosphoric acid reacts with magnesium hydroxide to produce magnesium phosphate and water via the following reaction:H3PO4 + Mg(OH)2 -----> Mg3(PO4)2 + H2O.Balance the equation, then enter the coefficients

5. Life orientation

Discuss ways in which xenophobia impacts on the community

6. chemistry

water and ammonia have different molar heats of vaporization. the best interpretation at the molecular level is that water molecules

7. maths

if sinA+cosA=1/5, then a value of tanA/2 satisfies which of the equation? a. 2x^2-x-1 b.x^2-2x-3=0 c.2x^2-5x-3=0 d. 2x^3-7x^2+2x+3=0

8. trig

If cos(t)=(-7/8) where pi

9. chemistry

Given the following data at 298K, calculate delta S for : 2Ag2O(s) -> 4Ag(s) +O2(g) deltaS(J/mol.K)121.3 42.6 205.2

10. Sciene

A Compound has 40 g of calcium and 160 g of bromine. What is the mass ratio of calcium to bromine in the compound?

11. Chemistry

Calculate the molar entropy of vaporization for liquid hydrogen iodide at its boiling point -34.55 degrees celcius. HI(l) HI(g) deltaHvap = 19.76 kJ/mol

12. physics

A softball of mass 0.220 kg that is moving with a speed of 4.0 m/s (in the positive direction) collides head-on and elastically with another ball initially at rest. Afterward the incoming softball bounces backward with a speed of 1.8 m/s. a) Calculate the

13. statistics

10.15 A psychologist theorized that people can hear better when the have just eaten a large meal. Six individuals were randomly assigned to eat either a large meal or a small meal. After eating the meal, their hearing was tested. The hearing ability scores

14. Chemistry 1

You carefully weigh out 17.00g of CaCo3 powder and add it to 68.85g of HCl solution. You notice bubbles as a reaction takes place. You then weigh the resulting solution and find that it has a mass of 78.88g . The relevant equation is CaCo3(s)+ 2HCl(aq)--->

15. trig

how much force is necessary to stop a 2500 pound car from rolling down a 40degree slope

16. Physics

An object is placed 30mm in front of a lens. An image of the object is located 90mm behind the lens. a) Is the lens converging or diverging? explain. b) What is the focal length of the lens? c) Draw a diagram with lens at x=0, locate the image. d) Is the

17. chemistry

A sample of argon gas occupies a volume of 295ml at 36 C. What volume will the gas occupy at 55 assuming constant pressure?

18. math

You are given the probability of event E. Find the odds in favor of event E and the odds against event E. a. 1/8 b. 2/5

19. algebra

Yolanda's yogurt house offers 3 different kinds of yogurt and 13 different kinds of toppings. How many different yogurt and topping combinations are possible?

20. economics

4. What source of economic growth is reflected in the economy by an increase in productivity without an increase in land, labor, or capital? A. technological progress B. foreign trade C. population growth D. savings and investments

21. Trigonometry

verify the identity: 1- (cos^2x)/(1-sinx)= -sinx

22. chemistry

Given the following data at 298K, calculate delta S for : 2Ag2O(s) -> 4Ag(s) +O2(g) deltaS(J/mol.K)121.3 42.6 205.2

23. Empirical Probability

Explain how empirical probability can be used to determine whether a die is “loaded” (not a fair die).

24. Math

In a geometric series, t1=12 and S3=372. What is the greatest possible value for t5? Justify your answer.

25. Form a polynomial f(x) from coefficient and it's 0

Form a polynomial, f(x), with real coefficients having the given degree and zeros. Degree: 4; zeros: 6i and 7i I completely don't know what to do with this problem... if someone can solve and give a good explanation, I'd appreciate it. Thanks.

26. pre- algebra

The perimeter of a triangle is 24 cm. One side is 2 cm longer than the shortest side. The longest side is 2 cm less than twice the length of the shortest side. Find the length of each side of the triangle.- write equation and solve.

27. physics

a cyclist travels a distance of 4km from p to q and moves a distance of 3km at right angle to pq .find his resulted displacement graphically

28. physics

suppose a particular atom has only two allowable electron orbits. how many different wavelength photons (spectral lines) would result from all electron transitions in this atom? 1. three 2. four 3. None of these 4. one 5. two please help..

29. algebra

How many ways can the offices of president, vice-president, treasurer, secretary, parliamentarian, and representative be filled from a class of 30 students?

30. math

Lighting hit a tree three-eighths of the distance up the trunk from the ground and broke the tree so that its top landed 40 feet from the base of the trunk. How tall was the originally tree?

31. math

37. A person deposited \$500 in a savings account that pays 5% annual interest that is compounded yearly. At the end of 10 years, how much money will be in the savings account?

32. algebra

how to write 6000 in scientific notation without exponents

33. Trigonometry

Verify the Identity: (1-cosx)(1+cosx)=sin^2x

34. spanish

What does " Que estudias tu" mean in spanish?

35. physics

a 1500 kg car travelling at 16.7 m/s to the south collides with a 6300 kg truck that is initially at rest at a stop light. the car and the truck sticks togetherand moves together after the collision. what is the final velocity of the two-vehicle mass?

can you help me please for this solving problem below... problem: A, B and C shared the profit of Rs. 9,00,000 in the ratio of 2:2:1 without providing for interest on B’s loan, B granted a loan of Rs. 4,00,000 in the beginning of accounting year. Where

37. life orientation

name two institutions in south africa that are involved in supporting or giving redress to these water pollution disasters.explain how these organizations are involved in providing a safe and healthy environment.

38. Math

What is the solution to the system? x+y+z=-8 x-y-z=6 2x-3y+2z=-1

39. ALGEBRA2

What is the value of k in the equation 6X^2 plus KX-10 equals (3X plus 2)(2X-5)

40. Trigonometry

(1+ tan^2x)/(secx)

41. Algebra 2

1. A rectangle has an area of x3 + x2 – 7x + 2 square meters and a width of x – 2 meters. Find its length.

42. history

During and after the Revolution, why did the emancipation of slaves proceed very slowly in the northern states?

43. Statistics

if 25% of all students asked say they spend too much time on homework, and 12 students are selected at random, what is the expected number of students who say they spend too much time on homework?

44. physics

a sound wave has frequency of 631 Hz in air and a wavelength of 0.54m. what is the temperature of the air? assuming the velocity of sound at 0 degree celcius is 334 m/s. answer in units of celcius.

45. physics

Two forces,F1 and F2, act at a point. F1 has a magnitude of 8.00 N and is directed at an angle of 56.0 degrees above the negative x axis in the second quadrant. F2 has a magnitude of 5.00 N and is directed at an angle of 52.9 degrees below the negative x

sin x= -1

47. Math

Solving systems of equations with three variables? What is the solution to the system? 1] x+y+z=-3 2] 3y-z=4 3] 2x-y-2z=-5

48. Algebra II

What is the solution to the system? 2x+y=9 x-2z=-3 2y+3z=15

50. Math

A design on a balloon is 2 cm wide when the balloon holds 47 cm^3. How much must the balloon hold for the design to be 6 cm wide? I'm confused about how to solve this. Could someone please show me the steps?

51. physics

A reciprocating compressor is a device that compresses air by a back-and-forth straight-line motion, like a piston in a cylinder. Consider a reciprocating compressor running at 150 rpm. During a compression stroke, 1.30 mol of air is compressed. The

52. english

find adverb in "This is one of the most democratic way to buy art. Online galleries can exhibit the work of hundred of artists specializing in many different genres including figurative, abstract, landscape , still life, sculpture and so on. This gives you

53. to Damon

Sorry had to adress this to you as you're the only tutor online right now, and I really need help. My teacher looked at my answers. And she said she still wants me to add more information, so Im having some troubles. Here is a Louis Riel Summation to the

54. trig

prove as an identity 1/1+sin(x) + 1/1-sin(x)

55. math

35. A person hired a firm to build a CB radio tower. The firm charges \$100 for labor for the first 10 feet. After that, the cost of the labor for each succeeding 10 feet is \$25 more than the preceding 10 feet. That is, the next 10 feet will cost \$125, the

56. english

what does this mean: His [Claudius'] primary role in the play is to spawn Hamlet's confusion and anger, and his subsequent search for truth and life's meaning. What do they mean by spawn? isnt dat fish eggs?

57. substance

How alcoholism is a human factor that may cause ill health ,accidents,crises or disasters

58. English

Can you please check these two sentences, please? Thank you 1) Nature ceased to be considered as a philosophical entity (concept?). It came to be felt as a real living being (real and living being) and to be described as it actually was. 2) The Romantics

59. fin534

In order to expand its business, Auto Parts Distributing, Inc., is considering the purchase of four pickup trucks at a total cost of \$180,000. The company expects to keep these trucks for four years, then sell them. The company expects these trucks to

60. Trigonometry

solve: tan x/2= sqrt3/ 3

61. math

true or false? the function f-1 (x)-x/9 is the inverse function of f(x)=9x

62. Physics

Acceleration due to gravity is 9.81 m/s/s. What is the weight (in Newtons) of a 97.96 kg mass?

63. Psychology

There are five major perspectives of psychology used to explain a human behavior and mental processes. These five perspectives that I am referring to are Neuroscience, Psychodynamic, Behavioral, Cognitive and Humanistic The instruction that I have in my

64. Trigonometry

verify the identity: 1-cos^2x/1-sinx= -sinx

65. physics

A rectangular loop with sides l and w are inside of a region with constant magnetic field B is pulled to exit the region with velocity v. a) find the magnitude of the net induced emf on the loop b) find the direction of the current induced on the loop

66. Math

what is PSU's (penn state university)"annual scholarship" i have to fill out the yearly tuition & the room and board amount which all equals to \$36,144. I need the annual scholarship amount but idk where to find that information...

67. maths

Help please. Solve the following equation. 9x+1=13+7x

68. Algebra 2

the demand for a new video game is given by the function p(x)= -x^2 + 5x +75. Correspondingly, the supply function for the same game is given by p(x) = 7x-9, where p represents the price per video in dollars and x represents the number of video games sold

69. Trigonometry

If tan theta= 3 and Pi

70. Trigonometry

2cos[x-pi/8]-sqrt2=0 Pi=3.141592654

71. find real and complex 0

Find the real and complex zeros of the following function. Please show all of your work. f(x) = x^3 + 2x^2 - 6x + 8

72. Trigonometry

2cos^2theta-3costheta+1=0 inerval [0,2Pi)

73. us history

doing a final review crossword and i cant figure these two out 1. Planned_____; creating products that would wear out over a given period of time ( _ _ _ _ _ _ n _ _ _ _ _ _) 13 letters 2. a clear indication of nation-wide voter support ( _ a _ _ _ _ e) 7

74. science

if removed from the life cycle, which of the following would have the greatest impact on the productivity of lawns. 1. robins 2. moles 3. toadstools 4. dandelions 5. microrganisms i think 4 b/c of the seedd that are easily blown away in the wind to

0.05 M KOH?

76. English----Novel

I am looking for a novel that's set in the 1980--1999 in Zimbabwe. Any recommendation is appreciated.

77. Math

Hi Ihave the solution and all thE steps for this question.:.but I am still having a hard time understanding it :( could somebody please help me walk through all the steps to this question? 1) assume that an average television costs \$425 now and that the

78. Pre Algebra

Four numbers are drawn from random tiles numbereed 0 through 9. What are the odds of drawing numbers 1 through four in any order?

79. Chemistry

which of the following 10 g samples will decay the most in 28 days? a.P-32 b.Kr-85 c.Fr-220 I-131 the answer is c.Fr-220 but i want to know why, please help

80. maths

what will come in blank y*y*y*_____________p times=________

81. chemistry

What are the steps to determine how much Nitrogen Gas can be produced from 32.5 grams of Sodium Nitrate?

82. Math

A square and four congruent rectangles are arranged in a larger square. The smaller square and each of the rectangles have the same perimeter.Determine the ratio of the length of a side of the larger square to the length of side of the smaller square.

84. Geometry

one of the ancient store pyramids in egypt has a square base that measures 145m on each side. the height is 108m. What is the volume of the pyramid?

85. math

Can one cake be split into portions of 1/3; 3/9; and 8/15 or why not?

86. math

Can one cake be split into portions of 1/3; 3/9; and 8/15? why or why not?

87. management

what is the four elements of financial management.

88. Trigonometry

verify the identity: (1-cosx)(1+cosx)= sin^2 x

89. pre-calculus

find the derivative of y=(3x+1)^2 y= square root 13x^2-5x+8

90. physics

A net force of 265 N will accelerate how much mass at 0.5 m/s/s?

91. Algebra 2

Whar number must be added to both sides of the equation to solve it by completeing the square? 3x^2+15x=9 (1)225 (2)25 (3)6.25 (4)5

92. english

The report was thorough.It saved the department several hundred dollars

93. Algebra

Find an equation of the line L that passes though the point (-2,4) and satisfies the condition. L passes through the point (3, 7/2)

94. physics

what would be the distance from the image to the mirror if the imge form the object to the mirror is 20cm and the focal length is 10 cm

95. Math

Express as a single term in simplest form: 5/2- radical 12

96. Trigonometry

Use Heron's formula: a=46 b= 52 c= 67

97. Trigonometry

Solve: 2 cos[x-ð/8]-sqrt2=0

98. Trigonometry

Solve: 2cos^2 theta - 3cos theta+ 1= 0 interval [0, 2ð)

99. Trigonometry

Solve triangle ABC: B= 60 degrees, C= 90 degrees a= 4 feet

100. English

Could you please check these sentences, please? I'm not sure about the rephrase. 1)In the first stanza the poet remembers wondering aimlessly and alone in the countryside. All at once he was amazed by the sight of a crowd of daffodils dancing ad fluttering

101. physics

What work is done when 6.0 C is moved through an electric potential difference of 1.5 V?

102. maths

i have fopur questions like this but don't undersand them. thanks Rearrange the formula a=(7/b+1)-4 to make b the subject

103. English

Is it a mistake to write "Nature ceased to be consideres "as" a real living being?" I included a few more sentences. Thank you. 1) In the fourth stanza the poet suggests that in order to hear the voice of nature we should be in a state of inner emptiness

104. MAT/116

I was just wandering if this was correct? 1. Your company is planning to spend no less than \$80,000 and no more than \$100,000 on a landscaping project, which will be used as a promotional park that promotes your toaster manufacturing company. Write an

105. maths

(400t-300)(400t-300)+(200t-100)(200t-100) complete the square showing all steps

106. Legal

What are some possible defences for the tort of negligence? Australian.

107. trig

Ok, so im brand new at trigonometry. If i have a right triangle with an acute angle of 30° an opposite side of 4 and a hypotenuse of x how do ii find x

108. Science

PRessure is measured in Pascals (Pa). What combination of units is the same as a Pascal? and When you exert a force on a fluid in a closed container, does the pressure increase, decrease or remain constant? I think it will increase, but I'm not totally

109. math

multiply then simplify by factoring. if possible √2 √6 =

110. solving systems of equations with 3 variables

What is the solution to the system? x-2y=1 x-3y+z=0 2x-2z=18

111. life orientation

how cancer impact on the teenagers

112. Mathematics

Hi, I don't like asking for help .. can someone check my work please ? In a biometric system under testing there are 500 users. 200 were legitimate users (authorised), and 300 were not ( unauthorised) At one threshold the system:- Shut out 10 individual

113. science

a person has a hert attack and her condition is stablised but due to inflamatiom in the lung she could not breath so a machine helps her to breath and now the lung inflamation is healing .Will she be able to breath on her own once the machine is cut off?

114. Math

The capital letter F can be formed by connecting the points (0,4)(5,4) (5,2)(2,2) (2,0) (4,0) (4,-2) (2,-2) (2,-7) nad (0,-7), in this order. Determine the slope of a line that passes through the origin and divides the letter F into two regions of equal

115. com

Can you please identify the adverbs and adjectives in the following paragraph. Having credit cards could get some people into serious debt. I had a credit card at one time. I learned the hard way about using credit cards. I was using it for anything and

116. Spanish

15. _____ le duelen mucho las piernas. a. Ernesto b. A los muchachos c. A Pablo d. El joven D?

117. Trigonometry

verify the identity: (sin^3x-cos^3x)/(sinx-cosx)=1+sinxcosx

118. Math

I don't know how to do this math 7n + 2 = 4n + 17

119. English

I forgot to include the following sentences. When I describe Wordsworth' conception of poetry, shall I use the present or the past? 1) Wordsworth believed poetry should deal with everyday situations or incidents and with ordinary people living in the

120. English-lord of the flies

Give five present day examples of similar characteristics or situations present in the novel lord of the flies.

121. Life Orientation

Institutions/community organizations that are involved in supporting or giving redress to substance abuse.

122. Algebra

Simplify. 2/3(4x/2x^2-1)+3(3/3x-1)

123. whole number

When stacking bags of dog food, the heaviest items should be placed at the bottom. Starting at the bottom, in what order should bags of dog food weighing 25 pounds, 20 pounds, 30 pounds, and 28 pounds be stacked?

124. math

the area of a circle inscribed in the triangle formed by the line with equation x+y=1 and the two coordinate axes can be written in the form pi(a+b(sqr.c)/d) compute the value of a+b+c+d

125. Trigonometry

If tan theta= 3 and ð

126. Trigonometry

Solve triangle SSA: A= 78 degrees, a= 30 b= 61

127. maths

how can i slove 5x-2(x-5)=15

128. US History

What does historical context mean?

129. psychology

1) What were some of the irrational beliefs and attitudes that the characters displayed?

130. Trigonometry

Solve SSA: B=12.1 degrees b= 15 a= 23.9

131. Trigonometry

Solve SSA: A= 78 degrees a= 30 b= 61

132. Research

hi Are there any good image searches or databases? Preferably databases. IE, not google please. Thank-you

133. Life oriantation

Human problem impacts on the community.

134. math

use the distributive property to multiply then if possible simplify the resulting expression √3 (√3- √21)

135. Math

Find m

2/3x+4 + 6/x+2

2/5x + 1/9

8 + x-4/x+3

139. math

perform the indicated operation 4√45- 6√125=

140. math

the launch window for a weather satellite is represented by the inequality |t-360| < 20 where t minutes is the time from the start of the countdown to the launch. If the countdown starts at 01:00, at what times can the satellite be launched?

how do you write the number 12,346,823 in expanded form

142. heart

were is the heart found in the human body

143. math

if i had a 66 in bim and my teacher puts a 100 in the grade book what will be mi grade

144. space

A water tower has to be equidistant from three communities. The communities are at positions (-25, 20), (-5, -40) and (15, 30). Find the coordinates of the point where the water tower should be built.

145. Math

A pyramid is inscribed in a cube whose volume is 52pi cm^3. The volume of a sphere is equal tpo the volume of this pyramid. Find the volume of a second cube whose edge is equal to the radius of the sphere.

146. spanish

What does " Que estudias tu" mean in spanish?

147. financial management

what are the four elements of financial management and how can i summerize them?

148. calculus

I need help with this calculus problem. H(S)=S/(1+S) If F 1/2, -1/2 & (a+1)? I can't figure out what this mean /?

149. psychology

What are some of the basic steps in developing a training program in an organization? In training, what are needs assessments and how are they used?

150. Calculus

Evaluate the definite integral from [0,4] 4x^2 dx, by using its definition as a limit of approximating sums. First, I solve analytically so I know the answer I am trying to reach: 4/3 * x^3 over [0,4] = 4/3 * 4^3 = 256/3 Now, by approximating sums, I can

151. where do you place the comas

The oil from Eucalyptus trees which are native to Australia is known for its medicinal properties

152. physics

With a focal length of 10 cm, and D zero is 20, 15, 25, and 5, what is the D one

153. check

How do I right a check for 1,400 dollars?

154. algebra

Anthony's family plants 15 trees each weekend. If t is the total number of trees planted and w is the number of weeks, what is the expression for the total number of trees, t, planted after w weeks.

155. Math

A cylindrical tank with radius 6 in. and length 12 in. is placed on its lateral face with bases perpendicular to the ground and then filled with water to a height of 9 in. When the cylinder is rotated to sit on one of its bases, the height of the water

156. math

I can't figure this out this problem.. estimate 20% of 131 by using 10%

157. Reducing fractions

how do i reduce 8/28

158. Life orientation

Derasice the style disease / behaviour and explain 5 (or more ) factors that contribute to the disease

159. world history

In what year did city-states become common in greece

160. trig

y = sin (3x-2pi)

161. Science

What are five ways that humans make an impact on the climate?

162. math

What do they mean when they say given angle and given side of a triangle???? I don't get this

163. science

can energy be lost or does it transfer somewhere else? I thought energy can be lost but i'm just checking.

164. geometry

one of the ancient stone pyraminds in egypt has a square base that measure 145m on each side. The hight is 108m. What is the volume of the pyramid?

165. Trigonometry

Solve SSA: B= 12.1 degrees b= 16 a= 23.9