# Posts by MathMate

Total # Posts: 11,744

**Science**

You're welcome! :)

*August 19, 2014*

**Science**

The independent variable is the amount of money offered, which in this case takes on only two values, $0 and $5. Evidently other experiments could be carried out to have varied incentives, assuming the teacher keeps the job long enough to do further experiments.

*August 19, 2014*

**Applied Programming**

Technically you do not need to ask for a 2D or 3D calculation because there is no overlap of the shape names. You will need a string of if-else-elseif-endif statements, or more conveniently a switch statement. Use the "default:" option in case the user feeds a wrong ...

*August 19, 2014*

**chemistry calculations**

It is given that the reaction at the given temperature is in equilibrium. Next check if the reaction is homogeneous: all gases, so homogeneous. Now denote the stoichiometric coefficients by a,b and c for the reactants and products respectively (all equal to 1 in this case). ...

*August 19, 2014*

**Basic Algebra**

This is more a riddle than math. In my opinion, it is hinged on the word "equally", which could mean equally to the dollar, or to the cent. Taking the first case: everyone has an equal number of dollars. Factoring 5130, we have as prime factors: 2,3³,5,19, which...

*August 19, 2014*

**maths**

If we assume that the ordered pairs (x,y) follow a linear rule y=ax+b, we will be able to solve for the rule using two of the ordered pairs, and use the third to check if the rule is appropriate. Thus, for the first ordered pair: y=ax+b => 14=180a+b .... (1) For the second ...

*August 17, 2014*

**MAth**

The question as it is has a large number of solutions. In general, optimization problems have an objective function, such as minimum cost, minimum surface area, etc. and subject to constraints, such as maximum number of fruits per box, or maximum sizes, etc. An example ...

*August 17, 2014*

**Precal**

Hint: look up triangle inequality. Basically, it says that the sum of the lengths of any two sides of a triangle is greater than or equal to the length of the third side.

*August 16, 2014*

**calculus**

The diagonals are obtained by the sum and difference of the two vectors: a+b=<-2,5>+<3,2>=<1,7> a-b=<-2,5>-<3,2>=<-5,3>

*August 16, 2014*

**Geometry**

A plot of the three lines L1, L2 and L3 may be viewed here: https://imagizer.imageshack.us/v2/500x300q90/674/pUzIJX.png

*August 16, 2014*

**Geometry**

This problem is very interesting, and as Steve pointed out, there are 4 circles each of which is tangent to all three lines. This prompted me to look for a general solution for all four circles. If we first examine the condition of tangency of a circle C: (x-a)²+(y-b)&...

*August 16, 2014*

**math**

You're welcome! :)

*August 15, 2014*

**math**

When the perimeter of the triangle is doubled, it is 24. The perimeter before it is doubled is therefore half of 24=12. An equilateral triangle is a triangle with three equal sides. Perimeter = 12 Number of sides of an equilateral triangle = 3 Can you find the length of each ...

*August 15, 2014*

**loyla**

There is a black and a white ball left in the bag after pulling out the first. Can you find the probability of pulling out a black ball from a bag containing one black and one white ball?

*August 15, 2014*

**physics**

Use ratios, 15 g : 0.1 L 75 g : x L solve for x by cross multiplication.

*August 15, 2014*

**physics**

Let maximum velocity be x then x/α+x/β=t Solving, x=t/(1/α+1/β) =αβt/(α+β)

*August 15, 2014*

**riddle?**

Is this a question or a riddle?

*August 15, 2014*

**Math: Equivalence Classes**

To explain in more detail, we would investigate the relation: (a-2d)=(c-2b) Transposing terms, we get the same relation as (a+2b)=(c+2d) Hence all elements (a,b) in the equivalence class would have the same sum a+2b. For example, if the sum is 10, we can have 4 elements: (2,4...

*August 14, 2014*

**Math: Equivalence Classes**

If you haven't read the following link, you can read it before reading on: http://www.jiskha.com/display.cgi?id=1407879480 The idea of solving parts (a) and (b) of the linked question is to establish a methodical way to solve (c) and (d). The typical approach to solving ...

*August 14, 2014*

**math**

Area of a square = (length of each side)² If each side is measured in inches, the area is in square inches, or in².

*August 13, 2014*

**statistics**

Start with a table: R=rain (20%), ~R=no rain (80%) W=windy (30%), ~W=not windy (70%) If rain and wind are independent, the combined occurrence is the product of the respective probabilities. Example: (a)P(R∧W)=.2*.3=0.06 (b)P(~R∧~W=0.8*0.7=0.56 (c)... Will leave (c) ...

*August 13, 2014*

**statistics**

Total number of males =25+10+8=43 Total number of clients = 100 Selection is random. => Probability, P(M) = 43/100 = 0.43 You can proceed with the remaining questions in the same manner.

*August 13, 2014*

**Math**

As Reiny pointed out, the rings and chirps will occur at the same time every 6 seconds, or at 6, 12, 18, 24, 30, 36,.... seconds. So which of the 4 choices will be a moment where the two sounds will occur together?

*August 13, 2014*

**math**

Draw a diagram on paper according to the given information, and the answer will be on paper.

*August 13, 2014*

**math**

You don't have to solve each one, and you don't even need a calculator if you understand the following rules for integer calculations: Multiply: only odd*odd will give odd power: only odd to any power will give odd Add/subtract: only odd±even will give odd. Note...

*August 13, 2014*

**phy**

The few problems you have posted at the same time indicates that you are in the process of learning how to draw a free-body diagram (fbd). Follow your instructor's directions to draw a fbd and identify the triangle to be solved. You should end up with a right triangle in ...

*August 13, 2014*

**Chemistry**

Ammonia is NH3. The mass composition is the ratio of atomic masses (AM) within the molecule, i.e. mass composition of nitrogen =AM(N)/(AM(N)+3AM(H)) =14.0067/(14.0067+3*1.0079) =0.822 approximately.

*August 13, 2014*

**ias question**

If the question were "how do we write 13 aug 2014 in 5 letters without using numbers." then see http://www.jiskha.com/display.cgi?id=1400681438

*August 13, 2014*

**math**

The factor theorem helps us to say that the possible integral roots are in the form of (x±k), where k is a possible factor of the constant term (12) divided by a possible factor of the leading coefficient (1). Thus for the given problem, the possible integral zeroes are &pm...

*August 13, 2014*

**Math**

Hints: It can be shown by calculus that the maximum area of a polygon enclosed by a fixed length of perimeter is a regular polygon, i.e. a polygon with all sides and interior angles equal. It follows from the above that the maximum area enclosed by a fixed perimeter is a ...

*August 13, 2014*

**Physics**

1 HP = 745.6999 W 4 HP = 2982.7996 W 4t = 4000 kg Use mgh=PΔt h=PΔt/mg =2982.7996*10/(4000*10) =0.75m approximately

*August 13, 2014*

**maths**

Correct! Well done! :)

*August 13, 2014*

**maths**

use proportions/ratios: 1 7/8 : 2 1/2 ≡ x : 4 Simplify ratios: 15/8 : 5/2 ≡ x : 4 15 : 20 ≡ x : 4 3 : 4 ≡ x : 4 Solve for x.

*August 13, 2014*

**math**

Use ratio/proportions: 5.58 : 318.76 ≡ x% : 100 Product of means = product of extremes 318.76*x% = 5.58*100 x% = 5.58*100/318.76 = 1.75% approx.

*August 13, 2014*

**fractions/math / Help!**

With what Reiny showed, there should be sufficient information to work out 425 by yourself as an exercise. I will give you another example, 525: 525÷5=105 105÷5=21 21÷3=7 since 7 is a prime we cannot go further. so 525=5*5*3*7=3*5²*7 You're ...

*August 12, 2014*

**collge sydney**

Hints: Kinetic energy of a rotating object is given by: KE = Iω² I is moment of inertia in kg-m² and ω is angular velocity in rad/s. 1 RPM= 2πradians/60 s = π/30 rad/s.

*August 12, 2014*

**Algebra**

Correct! Well done! :)

*August 12, 2014*

**math**

one-to-one (injection): every element in the codomain is mapped by at most one element of the domain. onto (surjection): every element in the codomain is mapped by at least one element of the domain. We can see that f(x) is both one-to-one but not onto, since f(1)=4, f(2)=7, ...

*August 12, 2014*

**Algebra**

(E)--- 8x-14 ----(G)--- 4x+1 ----(F) Since EF=59, => 8x-14+4x+1 = 59 Solve for x.

*August 12, 2014*

**MATH help please**

(a) An equivalence relation must satisfy the following three requirements: 1. reflexivity (a,b)R(c,d) is reflexive if (a,b)R(a,b)is defined. Since a-2d=c-2b ≡ a+2b=c+2d so (a,b)R(a,b) is defined since a+2b=a+2b Therefore R is reflexive. 2. symmetry R is symmetric if (a,b...

*August 12, 2014*

**math**

In general, days of the week advance one day per year (on the same day/month). For leap years, days from first of January to the 28th of February will jump TWO days if it is a leap year. For example, January 1st 1900 was a Monday. January 1st 1901 was a Tuesday (note that 1900...

*August 12, 2014*

**math**

Break up 6^8 => 2^8*3^8 10^6 => 2^6 * 5^6 Multiply together the odd factor of each number to get the largest odd factor of the product.

*August 12, 2014*

**math**

Original square area = n*n u² New dimensions: (n+m), (n-m) New area = (n+m)(n-m)=n²-m² u² Change in area = difference of above areas.

*August 12, 2014*

**math**

Song 1: 1,2,3,4 song 2: 5,6,7,8 song 3: 9,10,11,12 ... song 9: 33,34,35,36 ... song ?: 73,74,75,76

*August 12, 2014*

**phy**

Given a=<-1,-4,2> b=<3,2,-2> c=<2,-3,1> bxc= i j k 3 2-2 2-3 1 =<-4,-7,-13> so a.(bxc) =<-1,-4,2>.<-4,-7,-13> =4+28-26 =6

*August 12, 2014*

**Chemistry**

Start with writing a balanced equation: 4Fe3O4+O2 => 6Fe2O3 Then use stoichiometric coefficients and molar masses to solve the remainder of the problem.

*August 12, 2014*

**phy111**

We assume that the wind is blowing east at x km/h, represented by the vector <x,0> The truck is moving along the vector <p,q>, where sqrt(p²+q²)=70 km/h, or <sqrt(70²-q²), q> We also know that the resultant of the two velocities equals <...

*August 12, 2014*

**phy111**

In what direction is the truck moving, due south, south-west? Answers will vary depending on the direction.

*August 12, 2014*

**phy111**

Displacement=0 velocity=displacement/time =0

*August 12, 2014*

**Maths**

The solution of this problem is based on finding numerical values of parameters a and b in the PDF f(x). Recall that the given PDF is zero over the domain R except that f(x) is non-zero over (0,1). Therefore all integration should be performed from -∞ to +∞ but for...

*August 12, 2014*

**Math**

1. Total area = 30*20 ft² Let x=width of walkway, final area = (30-2x)(20-2x)=400 Solve for x. 2. Lawn area = 60*80 m² Final lawn width = x Pool area = (60-2x)(80 2x)=(1/6)(60*80) Solve for x.

*August 11, 2014*

**math**

Solve by elimination: Eliminate y by adding equation (3) to equation 1: 4x+z=12 Similarly, add 2*(3) to equation (2): 5x+5z=30 You can continue the elimination process to find x and z. Back-substitute to find y.

*August 11, 2014*

**math**

Use the binomial distribution, p=P(chemistry)=0.4 n=12 (sample size) r=number taking chemistry P(n,r)=nCr*0.4^r*(1-0.4)^(n-r) where nCr=n!/((n-r)!r!) is binomial coefficient. For probability of getting AT MOST 4 taking chemistry, add up all possible cases, i.e. 0,1,2,3,4, or P...

*August 11, 2014*

**college physics**

360 degrees in 27.3 days. Angular speed = angle/time 360 degrees / 27.3 days = ? degrees/day? If necessary, use conversion 1 day = 86400 seconds to find degrees/s.

*August 5, 2014*

**college physics**

Assuming the mass of 5kg is suspended freely, i.e. under influence of gravity, then the force (tension) on the wire is equal to 5g, where g=acceleration due to gravity, 9.8 m/s².

*August 5, 2014*

**Geometry**

The longest side is the hypotenuse, 6a+1 So use Pythagoras: (a+1)^2+(6a)^2=(6a+1)^2 and solve for a, reject all values of a≤0.

*August 5, 2014*

**statistics**

Number of children = 3 Possible number of boys = {0,1,2,3} X=number of boys - number of girls ={-3,-1,1,3} P(X)= probability of event X. b g X P(X) 0 3 -3 1/8 1 2 -1 3/8 2 1 1 3/8 3 0 3 1/8

*August 4, 2014*

**science (physics)**

Initial velocity v0= <1,2> a(t)=<0,g> v=∫a dt = <0,gt>+C => v(t)=<1, gt+2> x(t)=∫v dt = <t,(1/2)gt²+2t>+C Assume x(t)=<0,0> at t=0, then C=0 x(t)=<t, 2t+(1/2)gt²)

*August 4, 2014*

**PHYSICS**

radius of earth = 6378.1 km Assuming g is not affected by other heavenly bodies, then Newton's law of gravitation applies: g=GMm/r^2=k/r^2 (k=a constant) => g'r'^2=gr^2 r'^2=r^2(g/g') r'=r sqrt(g/g') =6378.1 sqrt(9.80/0.980) = 2.02*10^4 km approx.

*August 4, 2014*

**operating system**

In simple terms, a deadlock is a situation where two or more (minimum 2) processes are stubbornly holding on to a resource while waiting for another, creating a situation where certain resources are never available, and hence no work gets done for either of the processes. ...

*August 4, 2014*

**physics**

1 kW = 1 kJ/s Work done = 22 kW * 60 s = 22*60 kJ = 1320 kJ If the efficiency changes to 75% from 100%, the work done is reduced in the same ratio.

*August 4, 2014*

**math**

Assuming you are referring to the normal distribution, and depending on the context, it could be sample value, observed value, sample limit, etc.

*August 3, 2014*

**phy113**

Degrees fahrenheit = deg.C*(9/5)+32

*August 3, 2014*

**Geometry**

First find area of base: hypotenuse = 13 one leg = 12 other leg = √(13²-12²)=5 Area of base = 5*12/2=30 unit² Volume of prism =(area of base)*height/3 =?

*July 14, 2014*

**maths needed fastly**

I'll solve one, and will let you try the others as exercise. x=(4/5)(x+10) multiply by (5/4) on both sides: 5x/4 = x+10 subtract x from each side 5x/4-x =10 x/4=10 x=40 Check: (4/5)(x+10)=(4/5)(40+10)=40=x ok.

*July 12, 2014*

**mathe**

Let the cone radius = R cone height = H Let cylinder height = h then cylinder radius, r = R(1-h/H) Volume of cylinder, V =πr²h =πR²(1-h/H)²h For maximum volume, dV/dh=0 π(1-h/H)^2R^2-(2πh(1-h/H)R^2)/H=0 which simplifies to: (H^2-4hH+3h^2)=0 which ...

*July 12, 2014*

**physics**

Initial speed = 98 km/h = 98/3.6 m/s Work done = KE(final)-KE(initial) = (1/2)1370(0²-(98/3.6)²) = -508 kJ (approx.)

*July 11, 2014*

**physics**

Work done = F.D = 1.57*0 = 0 J.

*July 11, 2014*

**statisticss**

Calculate Z=(x-μ)/σ and look up the normal distribution table for the probabilities.

*July 8, 2014*

**physics**

First 30km with a speed of 30km/h means it took 1 hour. For an average of 40km/h over 60 km, total time = 60/40 = 1.5 hours. Time left for 30 km = 1.5-1 = 0.5 h. Can you calculate the speed needed for the second half of the journey?

*July 8, 2014*

**Physics**

Both correct!

*July 7, 2014*

**Physics**

Just answered your question a moment ago. Please check your previous post.

*July 7, 2014*

**Physics**

Correct for both.

*July 7, 2014*

**Physics**

Let initial velocity = vi final velocity = vf (negative if opposite in direction) Change in momentum, ΔM = m(vf)-m(vi)=m(vf-vi) a) Case A: vf=0, ΔM=-m(vi) Case B: vf=-vi, ΔM=-2m(vi) The absolute value of the change is greater in case B. b) Force = ΔM/&...

*July 7, 2014*

**math**

x=blue, y=green x/(25+x+y)=1/4 Cross multiply and simplify 4x=25+x+y => 3x-y=25 y/(25+x+y)=1/3 Cross multiply and simplify 3y=25+x+y => -x+2y=25 Solving: 5x=75 => x=15 y=3*15-25=20 z+15/(60+z)=4/13 Cross multiply 13(z+15)=4(60+z) 9z=45 z=5 5 blue beads must be added.

*July 7, 2014*

**math**

If the roots of a quadratic equation are equal, that means the discriminant equals zero, or b²-4ac=0 (for ax²+bx+c=0) So expand the expression and see if you can factorize the result to suit the conditions.

*July 5, 2014*

**Physics**

For the velocity, equation PE and KE. PE=KE mgh = (1/2)mv² and solve for v. (both g and h are negative, y is positive upwards) For time, use y=vi*t+(1/2)at² for vi=0, equation simplifies to y=(1/2)at² (Notice that both y and g are negative)

*July 2, 2014*

**PHYSICS**

Resolve forces into x,y components. Let the x-components of forces be f1,f2 then f1+f2=332 f1-f2=122 Solving f1=(332+122)/2=227 f2=(332-122)/2=105 Assuming θ=0 (in direction of raft) so the forces are 227 and 105N

*July 1, 2014*

**not statistics**

It depends on the tax rate, hence on where the payment is done. If the tax rate is 10%, then the sales tax is 993.91*0.10=$99.39

*July 1, 2014*

**physics**

average speed = total distance travelled / total time Total distance travelled = 30km/h * 0.5 h + 25km/h * 1 2/3 h + 40km/h *2 h = 136.667 km Total time = 0.5+1 2/3 + 2 = 4.1667 h Average speed = 136.667/4.1667 = 32.8 km/h

*July 1, 2014*

**physics**

Given: θ=arctan(3/4)=36.87° approx. m=0.5 kg μ=0.25 weight of block can be resolved into force down plane, F = mg sin(θ) and normal force, N = mg cos(θ) Let P be applied force parallel to plane (upwards) to maintain equilibrium, then Consider ...

*July 1, 2014*

**Physics**

Don't know how much work "I" do during this motion because I don't have the equations to calculations human work done during physical activities. However, work done on the 10N block is zero, the way you calculated it. When you lift the block, you are doing ...

*July 1, 2014*

**computer system organization**

Have you reviewed the three given sites as suggested? What are your thoughts about the quality of information supplied?

*July 1, 2014*

**Physics**

Nice question! Use energy. KE=PE+W Let x=distance up the slope (1/2)mv²=mg(sin(&theta))+μmg(cos(&theta))x Solving for x: x=(v²/((2g(sin(θ)+μcos(&theta))

*June 30, 2014*

**Statistics**

Use binomial distribution. P(r)=nCr*(p^r)(q^(n-r)) n=7 p=1/6 q=1-1/6=5/6 we need to calculate P(5)+P(6)+P(7) P(5)=7C5*(1/6)^5*(5/6)^2 =0.001875 P(6)=1.25*10^-4 P(7)=3.57*10^-6

*June 30, 2014*

**Algebra**

If you plot the graph, it will be a parabola concave up, with a zero at x=0, or x=4. Therefore f(x)≤0 when x∈[0,4). The correct answer would be S={x|x∈(-∞,0]∪[4,+∞)}

*June 30, 2014*

**mathematics**

Assuming garden has uniform width w. 2*60*50=(50+w)(60+w) => w²+110w-3000=0 w=22.62 or -132.62 (rejected) So wall is 22.62 m from the house.

*June 30, 2014*

**physics**

In the case of uniform acceleration, distance = average speed * time distance = 0.04m average velocity = (350+210)/2 m/s = 280 m/s Time = distance / average speed = 0.04/280 s = 1.43*10-.4 s

*June 30, 2014*

**math**

Out of 100 questions, 48 correct answers 11 blank 41 wrong answers total 100 We don't get to see the scheme. Assume the scheme says: 1 point for each correct answer, -1 point for each incorrect answer, 0 for leaving it blank. So total points =48-41-0 =7

*June 30, 2014*

**physics**

Acceleration = (vf-vi)/t = -2.24/2.55 = -0.8784 m/s Δx = vi*t + (1/2)at² =2.24(2.55)+(1/2)(-0.8784)(2.55²) = 2.85 m

*June 30, 2014*

**Geometry**

Have you read the Wiki article on cyclic quadrilaterals? It gives a lot of information on the subject. If it still does not answer your question, you could post your question and we could all learn something. http://en.wikipedia.org/wiki/Cyclic_quadrilateral

*June 29, 2014*

**physics**

For maximum height, equate PE and KE mgh=(1/2)mv² h=(1/2)37.1²/9.8=70.2 m at 50m, KE is reduced by mgh => (1/2)mv²=(1/2)m(37.1)²-mg(50) v=sqrt((37.1²-2(g)(50)) =19.9 m/s

*June 28, 2014*

**physics**

Conversion factor: 1 m/s = 3.6 km/h Δv=(vf-vi)=vi+aΔt 163 km/h = 163/3.6 = 45.28 m/s 45.28=vi+5.79*3.6 vi = 24.4 m/s = 88.0 km/h

*June 28, 2014*

**Physics**

Since gravity on the moon is about 1/6th of that on earth, the mercury column would be 6 times higher for the same air pressure. However, the atmosphere on the moon is about 10^13 time rarer than that on earth, the height of the mercury column is practically nil on the moon.

*June 28, 2014*

**math**

If the shapes are similar, area increase as the square of the ratio of the lengths. In this case, the shape remains the same, so old area = d*n new area = (1.1d)(1.1n) = (1.1)² dn = (1.1)² old area Percentage increase in area = 1.1²-1 = 21%

*June 28, 2014*

**statistics**

Given: μ=0.5" σ=0.01" Rejection rate = 0.8% = 0.008 rejection criterion = z<Z X=μ+Zσ =0.5+0.01Z From normal distribution tables P(Z<-2.409)=0.008 so X=0.5-0.01*2.409 =0.4758 Ans: washers with diameters less than 0.476 are rejected.

*June 28, 2014*

**Physics**

Power = work done / time = mgh / time = 55kg * 9.8 m/s² * 11 m ÷ (25*60 s) = 4.0 J/s = 4.0 W

*June 27, 2014*

**Physics**

During the reaction time of 0.59 s, car is still moving at 11 m/s, so distance to be added is 11 m/s * 0.59 s = 6.49 m. The deceleration is a=-8 m/s² vi=11 m/s vf=0 m/s (trying to stop) vf²=vi²+2ax => x=(vf²-vi²)/2a =(0²-11²)/(2*(-8)) = 7....

*June 27, 2014*

**physics**

Archimedes principle states that the buoyant force on an immersed object equals the mass of liquid displaced by the object. 230 ml of water weighs 230g Buoyant force = mg = 0.230 kg * 9.8 m/s² = 2.25 N

*June 27, 2014*