Sunday

July 24, 2016
Total # Posts: 35,337

**Math Help!**

remember, when you divide powers with the same base, keep the base and subtract the exponents, so 7^9/7^3 = 7^9 ÷ 7^3 = ...
*April 12, 2016*

**College Algebra**

No idea what the Malthusian model is, but I will do it my way P = 30,000 e^(kt) , where k is constant and t is years given:when t = 9, P = 60,000 30000 e^(9k) = 60000 e^(9k) = 2 9k = ln2 k = ln2/9 P = 30,000 e^((ln2/9)t) when is P = 1,000,000 ? 30,000 e^((ln2/9)t) = 1,000,000 ...
*April 12, 2016*

**Calculus I**

V = (4/3)π r^3 dV/dt = 4π r^2 dr/dt given: dV/dt = 8π , r = 1 8π = 4π(1) dr/dt dr/dt = 8π/4π = 2 A = 4πr^2 ----> (did you notice that surface area equals the derivative of volume ??) dA/dt = 8πr dr/dt when r = 1 dA/dt = 8π(1...
*April 12, 2016*

**Math Help!**

You are very welcome
*April 12, 2016*

**Math Help!**

correct for both
*April 12, 2016*

**Math Help!**

I noticed in your first question you have 4^a. None of the choices would match that. It had to be 2a(a^2 + 4a) to get a correct answer from your choices. You are using the distributive property which is illustrated by a(b + c) = ab + ac you multiply the stuff sitting in front ...
*April 12, 2016*

**Algebra**

Let the completed job be represented by 1 The first crew worked for 2 days, so they did 2/7 of the job. This leaves 5/7 of the job to be finished by the combined work of the two crews rate of first crew = 1/7 rate of 2nd crew = 1/5 combined rate = 1/7 + 1/5 = 12/35 let the ...
*April 12, 2016*

**Math**

XXXXXX 000901 This follows your wording, but a number such as 000901 would be 901, making it a 3 digit number. Does you number have decimals? then how about 901.000 ? Otherwise your question makes no sense
*April 12, 2016*

**Algebra**

Did you translate the English into Math? I said: x^2 = 4x + 60 now you have a nice and simple quadratic which factors. x^2 - 4x - 60 = 0 solve for x, and take only the positive result
*April 12, 2016*

**Math**

You obviously have a ||gram WXYZ where angle X = 113 In any parallogram, the opposite angles are equal and adjacent angles add up to 180 I don't know what <XYZ= <YZW= <ZWX= is supposed to mean. If 3 angles are to be equal then you must have a rectangle, which ...
*April 12, 2016*

**algebra**

see here http://www.jiskha.com/display.cgi?id=1460427888 Give yourself a nickname, so we can keep track of the questions and avoid duplication.
*April 11, 2016*

**EASY Pre-Algebra**

the four offices are defined and distinct. e.g, you could not simply interchange the office of the secretary with the office of the chairman So you have a permutation, since the order matters. Words such as "committee, select, choose" usually imply a combination
*April 11, 2016*

**Calculus Help Stuck Part 2?**

careful: what happened to your x's in (x-4)/(4-x) ? What really happened is this (x-4)/(4-x) = -1(4-x)/(4-x) = -1[ (4-x)/(4-x) ] = -1[ 1 ] = -1 Any number divided by its opposite = -1
*April 11, 2016*

**Calculus Help Stuck Part 2?**

Step1 for me in any limit question is actually sub in the approach value If you get a real number, that's your answer, all done! so for x = 4, we get 0/0, ok, we got work to do step: if you get 0/0 for simple rational expressions like the above, IT WILL FACTOR. Sometimes ...
*April 11, 2016*

**maths**

cosa = 12/13 construct a right-angled triangle and use Pythagoras to find the sides 5, 12, and 13 since the cosine is + in I or IV, we have two cases: case1: in quad I sina = 5/13, cosa = 12/13 seca + sina = 13/12 + 5/13 = 229/156 case2: in quad IV sina = -5/13, cosa = 12/13 ...
*April 11, 2016*

**interest rates computation**

first investment --- x 2nd investment ----- 4x .07x + .13(4x) = 7965 solve for x
*April 11, 2016*

**algebra**

Follow the same steps I showed you in the previous post Same kind of problem.
*April 11, 2016*

**algebra**

looks like everything is referenced in terms of quarters, so start with : let the number of quarters be x dimes ---- x+138 nickels ---- 2x pennies ---- 14x + 28 Now that you have the NUMBER of coins defined, we go for the VALUE of those coins 25x + 10(x+138) + 5(2x) + 1(14x+28...
*April 11, 2016*

**Math**

total ages = 60 Generally, if the mode is 8 would mean there are more than one age of 8 suppose there are two with age 8, leaving 44 for the other 4 (11 for the average of the remaining 4) could have 9 and 13, and 8 and 14 so we could have: 8,8,8,9,13,14 or we could have: 8,8,...
*April 11, 2016*

**Calculus**

go to your other post further up
*April 11, 2016*

**Calculus**

at x = 5, we get 20/0 which is undefined The limit does not exist (we only have work to do if the limiting value produces 0/0)
*April 11, 2016*

**Math**

Haven't seen anybody use tables out of "handbooks" in over 30 years, .... amount = 9000(1.08^20 - 1)/.08 = 9000(45.7619643) ---> last number should be in your handbook = $411,857.68
*April 11, 2016*

**Math**

A blue car cannot be on either end. So we have to start and end with a red car. They must be parked this way RBRBRBR number of way to do this is R-B-R-B-R-B-R 4x3x3x2x2x1x1 = 144
*April 11, 2016*

**Word problem middle school**

This looks like a GP with a = 4 r = 1.5 so cost = 4 + 4(1.5) + 4(1.5)^2 = ... I will let you do the arithmetic
*April 11, 2016*

**Bus. Math help!**

So PV = 80,000 i = .085/12 = .0070833333.... n = 12(25) = 300 payment = x x(1 - 1.00708333..^-300)/.00708333...) = 80,000 x = 644.18 which is none of the choices, D would come closest
*April 11, 2016*

**probability**

let m be the mean, and let s be the standard deviation (11 - m)/s = -3 11-m = -3s (16-m)/s = 3 16-m = 3s add them : 27 - 2m=0 m = 13.5 3s = 16-13.5 = 2.5 Using my favourite normal distribution calculator: http://davidmlane.com/hyperstat/z_table.html I get .305
*April 11, 2016*

**Math**

C is correct
*April 11, 2016*

**Calc**

If (a,b) is a point not on Ax + By + C = 0 then the shortest distance D from (a,b) to the line is D = |aA + bB + C|/√(A^2 + B^2) First change your equation into general form: 4x - 2y - 4 = 0 D = |1(4) + (-5)(-2) - 4|/√(16+4) = 10/√20 = 10/2√5 = 5/√...
*April 11, 2016*

**Math**

I will go with your definitions then 2πr + 4s = 9 s = (9-2πr)/4 total area = A = πr^2 + s^2 = πr^2 + (9-2πr)^2 /16 dA/dr = 2πr + (1/8)(9-2πr)(-2π) = 2πr - π(9-2πr)/4 = 0 for a max/min 2πr = π(9-2πr)/4 8π...
*April 11, 2016*

**Math**

This question is not as easy as it first appears. John found the number of ways to select exactly 3 coins from the 5 given. But it said at least 3 coins so we could have 4 or all 5 number of ways to select = C(5,3) + C(5,4) + C(5,5) = 10 + 5 + 1 = 16 But we have not yet ...
*April 11, 2016*

**Algebra 2**

For each of the given trig ratios, make a sketch of the corresponding right-angled triangles sinα = 12/13 , so y = 12, r = 13 x^2 + y^2 = r^2 x^2 + 144 = 169 x^2 = 25 x = 5 in quad I , so sinα = 12/13 , cosα = 5/13 cosβ = 21/29 in quadrant I x = 21, r=29 y...
*April 11, 2016*

**math**

Just do it. The instructions are quite clear.
*April 11, 2016*

**algebra**

for y = ax^2 + bx + c the x of the vertex is -b/(2a) so for yours, the x of the vertex = 16/8 = 2 I see (2, -7) as the only point where x = 2 I would now sub x = 2 into the equation to make sure I get -7
*April 11, 2016*

**Algebra 2**

Steve, as long as they are not imaginary.
*April 11, 2016*

**math**

The letters: AA RR NN G EE M T Number of arrangements = 11!(2!2!2!2!) = 2,494,800
*April 11, 2016*

**math**

let the number of students be 19x let the number of teachers be x 19x + x = 500 20x = 500 x = 25 There are 19(25) or 475 students and 25 teachers check: total = 25+475 = 500 ratio = 475 : 25 = 19:1
*April 11, 2016*

**calculus**

h = -16t^2 + 79t + 4 we need the vertex of this downwards parabola the t of the vertex = -b/2a = -79/-32 = 79/32 sec for that time height = -16(79/32)^2 + (79/32)(79) + 4 = 197.796.. = 197.80 correct to 2 decimals check my arithmetic
*April 11, 2016*

**Math HELP PLEASE QUICK!**

3.54x10^7 m /(3x10^8 m/s) = .118 seconds
*April 11, 2016*

**Calculus**

I will assume that you had y'' = 2(x-12)/x^4 f(x) will be concave up when y" > 0 and concave down when y" < 0 we don't have to worry about x^4, it will always be positive, except when x = 0 , which is a restriction on f(x) anyway. I don't see ...
*April 11, 2016*

**Calculus**

f(x) = ax^3 + cx^2 + d f'(x) = 3ax^2 + 2cx + 0 f'(-4) = 9 48a - 8c = 9 ** the point (-4,9) is on f(x) -64a + 16c + 6 = 9 *** 2 times ** ---> 96a - 16c = 18 *** ---------> -64a + 16c = 3 add them: 32a = 21 a = 21/32 in 48a - 8c = 9 48(21/32) - 8c = 9 -8c = -45/2 c...
*April 11, 2016*

**mathematics-root of cubic eqn**

let f(x) = x^3 + 2x^2 + 3x - 4 by trial: attempt x = ±1 , ±2, ±4 f(1) = 1+2+3-4 ≠ 0 f(-1) = -1+2-3-4 ≠ 0 f(2) = 8+8+6-4 ≠ 0 f(-2) = -8 + 8 - 6 - 4 ≠ 0 f(4) ≠ 0 f(-4) = -64 + 32 - 12 - 4 ≠ 0 There are no nice rational ...
*April 11, 2016*

**Math**

The 300 would be correct if he gave no discount So his final selling price has to be P300 let the marked price be x so .6x = 300 x = 300/.6 = 500 check: the marked price is 500 giving a discount of 40%, which is 200 means that he sells at 300 profit = 300-200 = 100 percentage ...
*April 11, 2016*

**Math**

distance of 1st bounce --- 8 distance of 2nd bounce --- 2(4) = 8 distance of 3rd bounce --- 2(2) = 4 distance of 4th bounce --- 2(1) = 2 distance of 5th bounce --- 2(1/2) = 1 distance of 6th bounce --- 2(1/4) = 1/2 distance of 7th bounce --- 2(1/8) = 1/4 distance of 8th bounce...
*April 11, 2016*

**@ Anonymous**

If you are going to give a detailed solution, then you should not gloss over the critical part of your solution: SO Equation 1 X + (6/X) = 5 X=2 or else you might just as well state the obvious solution at the beginning.
*April 11, 2016*

**math**

2 and 3 just sort of popped into my mind.
*April 11, 2016*

**Math**

Your distance of 450.69 miles is correct However, the angle of 17.43 is the angle within the triangle. You must add the original direction of 27 degrees to get S 44.3 E
*April 11, 2016*

**Math**

After you make your sketch, and after you enter your angles, you should realize that the plane makes a 90 degree turn. So you just have a right-angled triangle. Use Pythagoras to find the distance. Let the angle opposite the 135 side be θ then tanθ = 135/430 θ...
*April 11, 2016*

**Math: Trigonometry**

ahhh, missed the part where we want the sum of the first 3 π/12 + 5π/12 + 7π/12 = 13π/12
*April 10, 2016*

**Math: Trigonometry**

4cos^2(2x-pi) = 3 cos^2 (2x - pi) = 3/4 cos (2x-pi) = ± √3/2 I know that cos 30° = √3/2 so 2x - pi = pi/6 2x = pi + pi/6 x = 7pi/12 ---->105° since we had cos(2x-pi) = ± √3/2 2x - pi could have been in any of the 4 quadrants 2x - pi...
*April 10, 2016*

**Geometry**

simplest way: Heron's Formula A = √(s(s-a)(s-b)(s-c)), where s = (1/2)the perimeter. s = (1/2)(15 + 15 + 8) = 19 s-a = 19-15 = 4 s-b = 19-15 = 4 s-c = 19-8 - 11 area = √(19(4)(4)(11) = √3344 = appr 57.83 2nd way: works in this case because it is isosceles...
*April 10, 2016*

**math**

First let's choose the books top shelf = C(6,4) = 15 middle shelf = C(3,2) = 3 bottom shelf = C(6,3) = 20 so he can read 15x3x20 or 900 different combinations of 9 books Now for each of the choices of 9 books, he can read them in 9! ways. so the number of ways he can read ...
*April 10, 2016*

**math**

ahh, behold the beauty of the metric system 130 mm = 13 cm
*April 10, 2016*

**Math**

Don't know what you mean by "I had to make prisms out of construction paper of the same size". Did you mean the same volume? , the same height? What stays the same?
*April 10, 2016*

**Trig**

you need to sketch right-angled triangles to get the missing sides given: sinx = -1/4, y = -1, r = 4 x^2 + y^2 = r^2 x^2 + 1 = 16 x = -√15 in III So sinx = -1/4 , cosx = -√15/4 , tanx = 1/√15 given: cosy = -4/5, x = -4, r = 5 then y = -3 siny = -3/5, cosy = -...
*April 10, 2016*

**algebra**

So this flagpole is almost 4 miles high? WOW And the cables are attached almost 2 miles from the base of this massive flagpole?? Check your typing, I bet you dropped a decimal point or something.
*April 10, 2016*

**Math**

Other than the fact that you can't bushwhack on the Appalachian Trail, we have a clear cut case of using the cosine law: let the distance back be x miles x^2 = 8^2 + 10^2 - 2(8)(10)cos113° = 273.40... x = 16.534.. (don't round off your calculator answer) now by the...
*April 10, 2016*

**Math**

#1, correct #2, to be horizontal, they must have the same y to be vertical, they must have the same x So, do you wish to change your answer?
*April 10, 2016*

**Math**

assuming that numbers and letters can be repeated ... number of cases = 26x10x10x10x26 =
*April 10, 2016*

**Trigonometry**

for each one, use the CAST rule to find where else a certain trig ratio is positive or negative for #1, you have found the angles in quadrant I, but the tangent is also positive in III, (the T of CAST) So è = 30 degrees in I ---> pi/6 or è = 210 in III ------ ...
*April 10, 2016*

**interest**

no time given for the first part. 2nd part: 500(1.04)^n = 1000 1.04^n = 2 take log of both sides n log 1.04 = log 2 n = log2/log1.04 = 17.67 years or n = 17.7 years correct to one decimal
*April 10, 2016*

**Geometry**

confusing question. Where does A come from. your 4 points R,S,T,U do not form a parallogram What are Rec1 etc ?
*April 10, 2016*

**math**

I know that Sixteen tons will get you another day older and deeper in debt
*April 10, 2016*

**Math**

Just did this less than an hour ago http://www.jiskha.com/display.cgi?id=1460275337
*April 10, 2016*

**Maths**

volume = pi r^2 h plug in your numbers, your r = .8
*April 10, 2016*

**Math**

a) for 25 therms cost = $.6686(25)) = $16.72 b) cost = 16.72 + (45-25)(.8587 = $33.89 c) cost = (x-25)(.8587) + 16.72 , for x > 25 or = .6686x , for 0 < x ≤ 25
*April 10, 2016*

**math**

morning of day 1 -- 3 ft evening of day 1 -- 1 ft ,(3-2) morning of day 2 -- 4 ft evening of day 2 -- 2 ... morning of day 27 -- 29 ft evening of day 27 -- 27 ft morning of day 28 -- 30 ft He has reached the top, no sliding back He will reach the top on Feb 28th
*April 10, 2016*

**maths**

a+11d - (a + 2d) = 36 9d = 36 d = 4 term(16) = a+15d = 64 a + 60 = 64 a = 4 so a = 4, d = 4
*April 10, 2016*

**Math**

between √13 and what ? And zero? since √13 = appr 3.6 that would be {1,2,3} correct your typing otherwise.
*April 10, 2016*

**Calculus (30min before deadline help pls )**

Make a sketch. Let the length of the girl's shadow be x let her distance from the lamp be y so you have 2 similar triangles: 5/x = 16/(x+y) 5x + 5y = 16x 5y = 11x 5 dy/dx = 11 dx/dx dy/dx = 11/5 so her shadow is increasing at 11/5 ft/sec or2.2 ft/sec but it is moving at 11...
*April 9, 2016*

**Calculus**

Make a sideview sketch let the radius of the cone be r cm let the distance from the base of the cone to the centre of the circle be h So the height of the cone is h+10 cm draw a radius from the centre to the base of the cone, it will be a right triangle r^2 + h^2 = 100 r^2 = ...
*April 9, 2016*

**Algebra**

time = distance/rate let her rate on the first trip be x mph 6/x + 6/3x = 2 each term by 3x 18 + 6 = 6x x = 4 she went out at 4 mph, and came back at 12 mph (12 mph for 6 miles in a kayak???, Wow!!)
*April 9, 2016*

**Math**

prob(defective) = 4/12 = 1/3 prob(not defective) = 2/3 a) prob(both defective) = C(2,2) (1/3)^2 = 1/9 b) one defective: = C(2,1)(1/3)(2/3) = 2(2/9) = 4/9 c) at most 1 is defective ----> rule out both defective, which we did in a) so Pro(of at most 1 defective) = 1 - 1/9 = 8...
*April 9, 2016*

**Math**

Do you know what a scale factor is? e.g. there are 12 inches in a foot so if we have a patio which is 10 ft by 14 ft, I could make a drawing where 1 inch repesents 1 foot. My scale factor is 12 so I would draw my patio as 10 inches by 14 inches In our case the scale factor is ...
*April 9, 2016*

**Calculus**

let the width be x and the length y , were the brick wall is along the length. the xy = 102 y = 102/x Cost = 50(2x) + 50y + 60y = 100x + 110y = 100x + 110(102/x) = 100x + 11220/x d(cost)/dx = 100 - 11220/x^2 = 0 for a min of cost 11220/x^2 = 100 100x^2 = 11220 x^2 = 11220/100 ...
*April 9, 2016*

**Probability**

prob(success) = 3/4 prob(fail) = 1/4 prob(2 of 11 to fail) = C(11,2)(1/4)^2 (3/4)^9 = .258 check my arithmetic
*April 9, 2016*

**Mathematics**

write it up this way: 9-5[8-3]*2+6 = 9 - 5[5]*2 + 6 = 9 - 50 + 6 = -35 I have no idea what happened in your "second" step
*April 9, 2016*

**math**

time for first car --- t hours time for 2nd car ------ t+2 hrs distance covered by first car = 55t miles distance covered by 2nd car = 40(t+2) 50t - 40(t+2) = 10 50t - 40t - 80 = 10 10t = 90 t = 9 the first car went for 9 hrs, and the second went 11 hrs. check: distance ...
*April 9, 2016*

**algebra**

I have no idea what this means. Are you solving some equation? What is the original equation?
*April 9, 2016*

**LOGARITHM**

totally unreasonable answer some number squared has to be 7 so a quick mental check would be (2(17) - 1)^2 = 33^2 = 1089 , certainly not 7 this is a standard quadratic, which is in a nice form (2x-1)^2 = 7 2x-1 = ± √7 2x = 1 ± √7 x = (1 ± &#...
*April 9, 2016*

**Logarithm**

I answered this further up the listing
*April 9, 2016*

**Logarithm**

Ln2+Lnx=1 ln(2x) = 1 by definition of ln e^1 = 2x x = e/2
*April 9, 2016*

**Math: Parametric Equations**

does this help? https://www.wolframalpha.com/input/?i=plot+x+%3D++cos(4t),+y+%3D+sin(6t)
*April 9, 2016*

**MAth**

let n be the number of half-years i = .072/2 = .036 73,000(1.036)^n = 100,000 1.036^n = 1.36986... log both sides and use log rules n log 1.036 = log 1.36986.. n = 8.898.. half-years = appr 4.45 years
*April 9, 2016*

**algebra**

number of whites --- x number of yellows --- 18-x 995x + 1250(18-x) = 22245 (I changed the $'s to cents) solve for x, has to come out as a whole number
*April 9, 2016*

**Canadian finances**

I have placed *** behind my choices. If you see no *** or no comment, I agree with your answer. which of the following services do banks not provide? a. lines of credit b. health insurance *** c. currency exchange d. none of above (THIS ONE) which institutions does not offer ...
*April 9, 2016*

**Math**

x(x+5) = 350 x^2 + 5x - 350 = 0 too bad it doesn't factor. By the formula x = (-5 + √1425)/2 = appr 16.37 ft take over remember perimeter = 2width + 2length
*April 9, 2016*

**math**

i = .038/365 n= 365(4) = 1460 principal = 3500 amount = 3500( 1 + .038/365)^1460 = 4074.53 So interest earned = 4074/53-3500 = 574.53 which is choice a)
*April 9, 2016*

**Geometry**

width ---- x length ---- 2x+5 x(2x+5) = 1375 2x^2 + 5x - 1375 = 0 solve the quadratic hint: it factors, but it may be just as fast to use the formula
*April 9, 2016*

**Precalculus**

How about this way: Since AC supports a 45 degree angle at the circle, AC must support a 90 degree angle at the centre. let the radius be r r^2 + r^2 = 8^2 2r^2 = 64 r^2 = 32 Area = pi r^2 = 32 pi or appr 100.53 Notice just as Damon pointed out, we don't even need to know ...
*April 9, 2016*

**karki**

let the AP be a, a+d, a+2d so 3a + 3d = 45 a+d = 15 ---> d = 15-a and a(a+d)(a+2d)=300 a(a^2 + 3ad + 2d^2) = 300 a(a^2 + 3a(15-a) + 2(15-a)^2) = 300 a(a^2 + 45a - 3a^2 + 450 - 60a + 2a^2) = 300 a(- 15a + 450) = 300 -15a^2 + 450a - 300 = 0 a^2 - 30a + 20 = 0 a = (30 ±...
*April 9, 2016*

**Trigonometrt**

sin ( 810- theta) I am sure you meant: sin(180 - θ) which is sinθ cot(θ - 360) .... recall that tan(-x) = -tanx and tan(360-x) = -tanx and of course the cot behaves just like the tan cot(θ-360) = -cot(360-θ) = -(-cotθ) = cotθ cos(-180 - θ...
*April 9, 2016*

**Probability (Math)**

You are correct
*April 9, 2016*

**math**

Since Mathematics is a precise language, it requires precise and correct English to express a problem to be solved. Please re-type your problem using correct and proper English so that it makes sense to me. "Texting" English doesn't cut it.
*April 9, 2016*

**gemoetry**

I don't see any diagram but by a simple trig ratio, we have cos 75.5 = 20/L L = 20/cos75.5 = appr 79.9 ft Wow, a ladder to go up about 8 stories high???
*April 9, 2016*

**Math**

If x = 2√2 and x = -2√2 then two of the factors are (x - 2√2) and (x + 2√2) or (x^2 - 8) must be a factor of your polynomial. Do a long algebraic division to get x^4+4x^3-4x^2-32x-32 = (x^2 - 8)(x^2 - 4x + 4) we can get more roots from x^2 - 4x + 4 = 0...
*April 9, 2016*

**math**

Just replace the units with their equivalents. 24 miles / 1 hour = 24*1760 yards / 60 minutes = (42240/60) yards/min = 704 yards/min I agree with your answer
*April 9, 2016*

**MATH**

I agree with your equation and I get $4011.25. Beyond that, I can't help you since I don't know what you mean by "syntax" error.
*April 9, 2016*

**I NEED HELP!!!**

arrange it in more standard form 2x^2 + 6x - 5 = 0 use the formula: x = (-6 ± √76)/4 = (-6 ± 2√19)/4 = (-3 ± √19)/2
*April 9, 2016*

**Algebra**

you are basically looking for the vertex of this downwards opening parabola the t of the vertex is -b/2a = -64/-32 = 2 seconds it will take 2 seconds to reach the maximum height when t = 2 h = -16(4) + 64(2) + 9 = 73 ft
*April 8, 2016*

**Algebra**

the real parts of the left side must match the real parts of the right side, and the imaginary parts .... your steps are correct, so x = -4, y = 1
*April 8, 2016*