Thursday

March 5, 2015

March 5, 2015

Total # Posts: 10,946

**Statistics**

The "68-95-99.7 rule" represents the two-tail probability of data within ±1,2 and 3 standard deviations respectively. For example, the probability of picking a value X from a normal distribution within the range μ-σ<Xμ+σ is approximately 68%. ...
*December 2, 2014*

**MATHS - ratios**

use ratios: 60 km / 1.5 hours = 100 km /x hours x=1.5 hours * (100/60) = ?
*December 2, 2014*

**3rd grade math**

subtract each number from the next number, and make your guess from there!
*December 2, 2014*

**math**

P=2πsqrt(L/g) dP/dL = 2π(1/2)L^(-1/2)/sqrt(g) =2πsqrt(L/g)/(2L) transpose appropriate terms: 2*[dP/(2πsqrt(L/g))] = [dL/(L)] Each term in square brackets is equal to the fractional form of percentage error, thus proved. (use Δ => differentials instead of ...
*December 2, 2014*

**math help!**

Add -2-2w to each side to get w=10. Put w=10 back into each side of the original equation to verify that you get the same value on each side (=32).
*December 2, 2014*

**Ashworth college**

I believe the "68-95-99.7 rule" means the percentage of observations within 1-2-3 standard deviations from the mean. Try to apply the rule to answer the given question.
*December 2, 2014*

**physics**

This problem is similar to the previous. Again, use conservation of energies.
*December 2, 2014*

**physics**

Since friction is negligible, use conservation of potential and kinetic energies. KE (at bottom) => PE (at top) mv²/2 = mg*Lsin(θ) v=2,g=9.81,sin(θ)=1/2 Solve for L. I get 0.82m
*December 2, 2014*

**Physics**

Ideas: Conservation of energies also means: - energies are transformed from one form to another. Some are easier to exploit/recuperate than others. - total energy in universe is constant, but could be out of reach.
*December 2, 2014*

**Probability and Linear Math**

40% of total investment = 40%*500000 = 200000 This puts a ceiling on B, and a lower bound on A.
*December 1, 2014*

**physics**

Let A=30 kg boy B=40 kg boy Force = 50 N For boy A: Static Friction = mgμs=30*9.8*0.15=44.1N < 50N => Boy A is set in motion. Net force after kinetic friction = 50N-30*9.8*0.1N=5.9N Acceleration = F/m = 5.9/30=0.69 m/s² (backwards) For B, the 40kg boy Static ...
*November 30, 2014*

**Math**

What you'll need to do is 1. find the 3 intersections of the lines, which are then the vertices, (xa,ya), (xb,yb), (xc,yc). 2. Find the mid-points of each side using Mab=((xa+xb)/2, (ya+yb)/2), ... 3. Find the perpendicular bisector of each side by passing a line ...
*November 30, 2014*

**Chemistry Correction**

Correct, you should get 1.974*10^(-29) instead. If you do not get the above value, it could be: 1. you did not use the correct value of pi (such as 3.14, 22/7,...) 2. Your expression is missing many parentheses. Remember PEDMAS or PEMDAS which your calculator sticks to, but it...
*November 30, 2014*

**Please answer**

Here the population variance is not known, so use student-t distribution. A 95% (two-tail) confidence interval would include the limits. The value 1.96 comes from a T-value for 97.5% (half tail). x̄-Ts ≤ μ ≤ x̄+Ts where x̄=sample mean s=sample variance...
*November 30, 2014*

**Statistics**

Using Binomial probability function, we are looking for: P(280≤X≤300) =Σ C(300,r)p^r*(1-p)^(300-r) for r=280, 281, ...300, and C(300,r)=300!/((300-r)!r!) =0.00896+0.01530+0.02474+0.03777+0.05427+...+0.00004+0.0000 =0.98992 Using normal approximation with continuity...
*November 30, 2014*

**chem**

pKa=-log10Ka =-log10(6.3*10-8) =7.2
*November 30, 2014*

**statistics**

It all goes back to the definition and application of α and p-value. Read: http://www.statsdirect.com/help/default.htm#basics/p_values.htm for a detailed explanation.
*November 28, 2014*

**Math**

I=kS/d² where I=illumination, k=proportional constant >0 S=source strength >0 d=distance One light source is S, and the other is 4S. Let d=distance from weaker source, then 11-d =distance from stronger source. We have illumination as a function of d I(d) = kS/d²...
*November 28, 2014*

**math**

200 questions, 2 marks for good answer, -1/2 marks for wrong answer. Ajay answered all questions. If he didn't give any wrong answer, he would have got 400 marks. Each wrong answer will set him off 2.5 marks. If he got 360, he got (400-360)/2.5=16 wrong, therefore 184 ...
*November 28, 2014*

**physics**

v0=2.7 (package was rising) x0=11 x1=0 a=-9.8 x1=x0+v1*t+(1/2)at² 0=11+(2.7)t+(1/2)(-9.8)t² Solve for t to get t=1.8 sec.
*November 27, 2014*

**algebra**

First observation: People either liked the skin cream (x of them) or didn't like the skin cream (100-x of them). "80% of the people who liked the new skin cream also liked the new lip balm" that makes 0.8x liked new lip balm. "50% of the people who did not ...
*November 27, 2014*

**Math**

First factor the denominator: x^3+x^2+x=x(x^2+x+1) Then assume constants A, B and C as follows: (-5x^2-8x-3)/(x^3+x^2+x) = A/x + (Bx+C)/(x^2+x+1) The steps are to find constants A, B and C (the solution) by adding together the right hand side and comparing coefficients of each...
*November 27, 2014*

**mathematics of investment**

12% simple interest p.a. equals 0.12/365 simple interest per day. Principal=P10000 interest per day = P10000*0.12/365 =P3.28767 /day Time it takes to reach P700(=P10700-P10000) = P700/(P3.28767) = 212.9 days rounded up to = 213 days
*November 27, 2014*

**chemistry**

Not sure how you got 87! :) Start with PV/T=constant, where T is in °K. V1=1.75*10³L T1=(9.0+273.15)=282.15°K T2=(80+273.15)=353.15°K (ok to use excess significant digits for calculation, but reduce answer to appropriate number). since Pressure & amount of gas...
*November 27, 2014*

**Physics**

Principle of floatation: A floating object displaces its own weight of the fluid in which it floats. Volume of steel =Vs Mass of steel Ms = ρs*Vs Volume of mercury displaced, Vm = Ms / ρm Percentage of volume displaced =Vm / Vs If the steel block floats with bottom ...
*November 27, 2014*

**Microsoft Excel**

Excel is nothing but a tool to help us. It does not create a new rule for precedence, but follows what we learned in elementary school. In maths, the rules of precedence PEDMAS (or some variant) are: Parentheses Exponentiation Division/Multiplication Addition/Subtraction. They...
*November 26, 2014*

**geometry**

Start by drawing a diagram. If BC=BD, then ∠BDC=∠BCD=34° (angles opposite equal sides. Hence ∠CBD=180-(34+34)=112° ∠ABD=∠ABC+∠CBD=? Recall that ΔABC is equilateral.
*November 26, 2014*

**Geometry**

See other post.
*November 26, 2014*

**physics**

He saw penguins at his intermediate destination.
*November 26, 2014*

**Algebra**

a) Total: 640 feet Two short sides: 2x long side 640-2x b) Since long side must be positive, we have 640-2x≥0 c) Area = short side * long side A(x)=x(640-2x) d) find x such that 30000≤A(x)≤40000 Make a table that gives x and A(x), Hint: A(50)=27000 <30000 A(86)=...
*November 26, 2014*

**Stats Math 3**

(1) The sample distribution taken from a binomial distribution is approximately normal because sample/population size < 0.05 ("small" sample). Also a binomial distribution approximates a normal distribution when np>K and np(1-p)>K, where K ranges between 5...
*November 26, 2014*

**Stats Math 2**

Population has binomial distribution. sample mean is 144/300. Check that sample satisfies normal approximation and proceed as in your next post. Do not forget to apply continuity correction when approximating a discrete distribution (such as binomial) by a continuous ...
*November 26, 2014*

**STATS Math**

Same as your other post: http://www.jiskha.com/display.cgi?id=1417003909
*November 26, 2014*

**Chemistry**

CuCl2.2H2O See for example: http://en.wikipedia.org/wiki/Copper%28II%29_chloride for more details.
*November 26, 2014*

**chem**

You're welcome!
*November 26, 2014*

**chem**

If it is diprotic, then your equation in (2) is correct, and the molar ratio NaOH/C6H7O6 would be 2, and hence the answer in 4 would be halved, ... problem solved.
*November 26, 2014*

**chem**

1. Numerically correct. You will have to get used to citing answers to the correct numnber of significant digits, depending on the given information. Here, the correct answer would be 0.001811 M. 2. The neutralization reaction is not correct. Ascorbic acid has only 1 H+, so it...
*November 26, 2014*

**phy101**

If the box rolls on a horizontal floor with a constant velocity, then it is in dynamic equilibrium, and no external (horizontal) force is acting on it. Thus the floor does zero work on the box.
*November 26, 2014*

**INTRODUCTION TO PHYSICS**

Don't know. According to Google, the density of ethanol ("alcohol") is 789 kg/m³. So if the liquid has a density of 750 kg/m³, i.e. it is less than the density of ethanol, it must be something else. If ethanol is mixed with water, the density goes up, i...
*November 26, 2014*

**Math**

Yes, Steve is right. Thanks Steve. Oversight on my part.
*November 25, 2014*

**Math**

Thanks Steve. Oversight on my part.
*November 25, 2014*

**Math**

Final total number of balls =10+6+112=128 Half of them would be 64. You will need 64 white and 64 yellow. I'll leave you to figure out how many of each colour to add.
*November 25, 2014*

**statistics**

Here, assume equal tails, then p̂=(0.045+0.133)/2=0.089 So the required form read: p̂-0.044≤p̂≤p̂+0.044
*November 25, 2014*

**vectors( need answer asap)**

The centroid of a triangle is located at 2/3 of the length of any median. Median=(OA+OB)/2=<5,1> 2/3 from vertex (origin)=<10/3,2/3>. Another way: It turns out that the coordinates of the centroid of a triangle is the mean of the x and y coordinates of the vertices...
*November 25, 2014*

**vector**

See: http://www.jiskha.com/display.cgi?id=1416936762
*November 25, 2014*

**statistics**

To do this experiment, you need to collect data at your school, including number of pairs of shoes for each respondant. Number of men and number of women interviewed. The analysis can then begin with you have the data.
*November 25, 2014*

**statistics**

You need data before you can do the analysis.
*November 25, 2014*

**Filipino**

Use Google translate if necessary. https://translate.google.com/
*November 25, 2014*

**Filipino**

[subordinate conjunction?] Mangyaring isulat ang iyong kumpletong tanong sa Ingles. Hindi namin na makipag-ugnay sa Filipino. (Please write your complete question in English. We are not able to communicate in Filipino.)
*November 25, 2014*

**statistic**

(a) "Given that it is not found in box 1" means that it is not in box 1, so probability of finding it in box 1 is zero. (b) Conditional probability: P(A|B)=P(A∩B)/P(B). Event A: defective in box 2 Event B: defective not in box 1 P(A)=1 box out of k = 1/k P(B)=not...
*November 25, 2014*

**Algebra**

In case you have difficulties also with Q3, there is a good article that show you how to solve a similar problem step-by-step: http://www.trans4mind.com/personal_development/mathematics/series/polynomialEquationDifferences.htm
*November 25, 2014*

**Algebra**

Question 3 requires the polynomial model, say P(x) where x is the month, 1 for January, 2 for February, and so P(7) is the value for July. So if you have already found the polynomial for question 3, it is a question of substituting the proper month (July) to find P(July) as ...
*November 25, 2014*

**Physics**

To obtain the acceleration of 6 m/s², a minimum force of 43.02 N is required. So the question is either incomplete, or contains typos. Please check.
*November 25, 2014*

**Physics**

use F=ma, and a=v²/r where m=981 kg, r=625 m, and F=2433 N (unit not given, Newton assumed). Solve for v.
*November 25, 2014*

**calculus**

Given L1: r= [4,-3,5] + t[2,0,3], t∈R L2: r= [4,-3,5] + s[5,1,-1], s∈R We need to find the plane that contains both L1 & L2. (changed to uppercase to avoid confusion with 1). Notice that P0=[4,-3,5] lies in the given plane, in fact, it is the intersection point of L1...
*November 24, 2014*

**math**

First, I suspect you are missing parentheses in your equations. It is very easy to forget them when working with typeset fractions which contain implied parentheses in the numerator and denominator. I assume the equations are: (x-1)/k = (y-2)/2 = (z+1)/(k-1).....(1) (x+3)/(-2...
*November 24, 2014*

**statistics**

Hint: Correlation studies do not reveal causal relationships.
*November 24, 2014*

**Microbiology**

Make a table and everything would be clear. stock totVol concentration 2 4 32 (2*64/4=32) 2 8 16 (2*64/8=16) 2 16 8 2 32 4 Now if 2 mL of water are added to each, then concentration would be: stock totVol concentration 2 6 32 (2*64/6=21.3) 2 10 16 (2*64/10=12.8) 2 18 8 ... 2 ...
*November 24, 2014*

**MATH!**

Sorry, Reiny is right. What I calculated could be called "average rate of return". Effective rate is calculated for one year only. See: http://www.jiskha.com/display.cgi?id=1397777653
*November 24, 2014*

**MATH!**

Use compound interest formula: monthly interest, i = 0.06/12=0.005 period, n = 7*12=84 Principal, P=1000 (say) Future value =P(1+i)^84 =1000*(1.005)^84 =1520.370 Effective rate (= average interest per year) =((1520.370-1000)/7)/1000 =0.0743 p.a.
*November 24, 2014*

**physics**

Conservation of Momentum: m1u1+m2u2=m1v1+m2v2 m=mass u=initial velocity v=velocity after impact 1,2 objects, people. Since the person catches the mass, the common velocity after "impact" is v1=v2=v. Solve for v, since all other variables are known.
*November 24, 2014*

**Math**

See Reiny's answer : http://www.jiskha.com/display.cgi?id=1332900654
*November 24, 2014*

**now mr. damon, physics**

http://www.jiskha.com/display.cgi?id=1416876526
*November 24, 2014*

**now mr. damon, physics**

See other post, modify constants to suit given values. Give final answer to 2 significant figures.
*November 24, 2014*

**physics**

Breaking strength T=mg=33.8kg*9.8 N mass = 3.02 kg radius = 1.2 m velocity = v Tension on string S=mv²/r=3.02*v²/1.2 At breaking point, S=T 3.02*v²/1.2 = 33.8*9.8 Solve for v. I get 11.5 m/s
*November 24, 2014*

**physics, please help**

Please see other post, and check the heat capacity/other constants.
*November 24, 2014*

**physics**

Calculate Tf=Ti+ΔT
*November 24, 2014*

**physics**

use: ΣmcΔT=0 Silver: Ti=107, Tf=T, m=63.8kg, c=240 J/kg/°C Ice: mass=1 kg, Heat of fusion: 334000 J/kg (ΔT=0) 63.8*(240)*ΔT + 1*334000=0 ΔT = -334000/(63.8*240)=-21.8°C
*November 24, 2014*

**pt1420**

negation
*November 24, 2014*

**math calculus**

Writing in component notation, <1,0,0>=i <0,1,0>=j <0,0,1>=k and using rules ixj=k, jxk=i, kxi=j jxi=-k, kxj=-i, ixk=-j and the magnitude of all unit vectors is always one. Above reduces to <0,0,1>.<0,1,-3> + <1,0,-4>.<1,0,-4> - 8|ixk...
*November 24, 2014*

**Chemistry**

Both are correct! Good work!
*November 24, 2014*

**physics**

Question says "using Earth data as a starting point" but does not give the radius of the earth. It could be 6371km (from Google) or any other value with different accuracies. So you will decide which value to use, you just have to state the source.
*November 24, 2014*

**physics**

Assuming the mass distribution and average density of the super-Earth does not depart from our planet, then the radius will be increased by a factor of 10^(1/3)=2.154 approximately. Use whatever radius of Earth that is given to you or you can find.
*November 24, 2014*

**trig**

I guess we all started at the same time, and I am the slowest of us all! :)
*November 24, 2014*

**trig**

1. 4cos(x)-2=0 cos(x)=1/2 x=acos(x)=1/2 between 0 and 2π or π/3 or 5π/3 because cosine is positive in the first and fourth quadrants. 2. 3sec²(x)-4=0 3sec²(x)=4 cos²(x)=3/4 cos(x)=±(√3)/2 for cos(x)=+(√3)/2 x=π/6, 11π/6 cos(x...
*November 24, 2014*

**chemistry**

Ksp=[Pb]³[AsO4]²
*November 24, 2014*

**MATH**

It's not clear who received 9 pennies. Assuming Danni received 9 pennies, Carl got 9*3=27 pennies from Bev. Therefore Bev got 3*27=81 pennies from Al. Al had collected 81*3=243 pennies.
*November 24, 2014*

**business math**

I am not familiar with the rules of the contribution. My interpretation of the question tells me that the taxes are based on the total gross employee income, which comes to (14*640+3*720)*13 weeks (approx. unless leap year) = $ 144560 Based on the given tax rates, the taxes ...
*November 24, 2014*

**Math**

Correct! Use sine rule to solve for the value of sin(B)=0.7825 which translates to 51.5 or 128.5°.
*November 24, 2014*

**statistics - question incomplete**

question incomplete
*November 24, 2014*

**Physics**

(a) use conservation of momentum, note that after collision, there is a common velocity v1=v2=v m1u1+m2u2=m1v1+m2v2=(m1+m2)v m1,m2=masses of bullet and block u1,u2=initial velocities of bullet & block v1,v2=(common) velocity of bullet and block after collision. substituting ...
*November 23, 2014*

**Physics**

ω(t)=t³+2t rad/s note that ω(0)=0 rad/s. (A) Angular displacement =∫ω(t)dt [0≤t≤T] =[t^4/4+t^2] from 0 to T =T^4/4 + T² (B) The angular acceleration is obtained by differentiation of ω(t) with respect to t.
*November 23, 2014*

**physics please help**

Start with the conservation of energy (when friction/air resistance are absent). Kinetic Energy, KE = (1/2)mv² Potential Energy, PE = mgh m=mass, v=velocity, h=change in height, g=acceleration due to gravity. Conservation of energy states that without external forces and ...
*November 23, 2014*

**physics please help**

Angle of ramp, θ=tan-1(2/12) Minimum force required (without friction), F = 65(9.8)sin(θ). Friction force, f= 50N Efficiency = useful force / total force = F/(F+f)
*November 23, 2014*

**math,trigonometry**

Draw a diagram to show the height of the tower (36m), angle of depression (from horizontal)=25°. So tan(25°)=36÷width Solve for wideth.
*November 23, 2014*

**Statistics**

When μ and σ are known, the sample mean (x̄) has normal distribution so the statistic is Z=(x̄-μ)/(σ/sqrt(n)), where n=sample size=148. (a) Assuming a symmetrical confidence interval, we have α=0.003/2=0.0015. Looking up a normal probability...
*November 23, 2014*

**Probability**

If the three events are independent, then the probability of getting two given characteristics is the product of the probability of the individual events. Thus P(I∪N)=P(I)*P(N) (if I and N are independent) =(0.10*0.50)=0.05. Note: this probability may include those who are...
*November 23, 2014*

**Physics**

Momentum = mass*velocity Note that velocity is signed. Using subscript 1=before impact subscript 2=after impact. Here, mass=0.118 kg=m1=m2 v1=+3.14 m/s (towards bat) v2=-33.7 m/s (away from bat) Calculate the change in momentum, Δmomentum = m2v2-m1v1 and give answer in ...
*November 23, 2014*

**statistics**

As in your previous question, if we assume random arrival, all students have equal probability of arriving first. The probability of a female student arriving first is given by #of favourable outcomes ÷ total # of possible events.
*November 23, 2014*

**statistics**

Total number of students: 9+15+8+12=44 Total number of females: 15+12=27 The selection is random, so all students have equal probability of being selected. So the probability of selecting a female is 27/44. Convert to a fraction and round to the nearest hundredth (i.e. two ...
*November 23, 2014*

**algebra**

Let c=current speed, and b=boat speed in still water. Speed with current = 225/5=45 mph Speed against current = 225/9=25 mph, Set up equations: b+c=45 b-c=25 Solve for b and c. By the way, when you know the sum and difference of two variables, the variable with the larger ...
*November 23, 2014*

**algebra**

The equilibrium price is where the two lines meet, namely when the number of units the manufacturer is willing to sell equals the number of units the retailer is willing to buy, both at price p. So 20p-1500=x=-4p+900 Solve for p to get p=100 (and x=500)
*November 23, 2014*

**Chemistry**

2Al+Fe2O3 -> Al2O3 + 2Fe Since the coefficients of Al and Fe are both 2, so the amount of iron formed would be in the ratio of the atomic masses, namely 55.85/26.98 (approximatelyly).
*November 23, 2014*

**Physics**

The resultant velocity of two velocities at 90° (such as x and y) apart can be obtained by resultant=sqrt(x-component²+y-component²)
*November 23, 2014*

**physics - insufficient information**

There is not sufficient information to give a numerical answer.
*November 23, 2014*

**Statistics**

This is a case of choosing without replacement, and order does not count. Number of ways = nCr = n!/(r!(n-r)!) =16!/(4!12!)
*November 23, 2014*

**math**

When two planes intersect (such as the edge of a rectangular box), the intersection is a line (not a point). When two planes do not intersect(such a the top and bottom faces of a rectangular box), then they don't intersect at exactly one point.
*September 23, 2014*

**reference frames**

Taking the difference is the right approach. However, they are heading in different directions, so the velocities have different signs. Hope that helps.
*September 23, 2014*

**Math - correction**

Correction: The equation given above σ²=(sum of (xi-μ)²)/N applies to a population. C is correct if we interpret the data as a sample of the given population, in which case the standard deviation is given as: σ²=(sum of (xi-μ)²)/(N-1) = ...
*September 23, 2014*

**Math**

C is not correct. There is a choice which is close to the answer. The previous post shows how you can find the correct answer.
*September 23, 2014*

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