Tuesday

September 1, 2015
Total # Posts: 33,211

**maths,integration**

v = 4-t s = 4t - 1/2 t^2 + c s(0) = 5, so c=5, and s(t) = 4t - 1/2 t^2 + 5
*July 10, 2015*

**Algebra**

with interest rate r, continuous compounding for t years results in a growth factor of e^rt. So, you want e^5r = 4 r = ln4/5 = .277, or 27.7% Which formula were you using to get 11% ?
*July 10, 2015*

**Maths**

answered in related questions below.
*July 10, 2015*

**math**

you have two pairs of equal sides. So, the two sides you have are half the perimeter.
*July 10, 2015*

**precal**

There are lots of good Riemann Sum online calculators. This one is easy, though. The interval widths are 0.5, so all you have to do is evaluate 0.5(f(.5)+f(1.0)+...+f(3.0))
*July 9, 2015*

**math**

d$ = 100d¢ You want to convert dollars to whistles: 100d¢ * (w whistles)/c¢ = 100dw/c whistles The easiest way to do this kind of thing is to treat it as a conversion from one unit to another. You can always multiply by 1 without changing anything. Since w ...
*July 9, 2015*

**math**

The common denominator of all those fractions is 120. So, say there are 120 members Then 45 are R, 75 are D Also, 80 are men, so 48 are Dm. That leaves 75-48=23 Dw So, 23/120 are Dw
*July 9, 2015*

**math**

.08c = .12d 2c = 3d so, c+d = 3/2 d+d = 5/2 d or c + 2/3 c = 5/3 c Not sure what your choices are...
*July 9, 2015*

**Calculus Partial Derivatives**

ignoring all the stuff with F and f, I assume you meant y = f(x+at) + f(x-at) ∂y/∂t= f'(w)∂w/dt + f'(v)∂v/dt = a(f'(w)-f'(v)) ∂2y/∂t2 = a(f"(w)∂w/∂t - f"(v)∂v/∂t) = a^2(f"(w)+f"(v))
*July 9, 2015*

**chemistry**

14.8/.917 g
*July 9, 2015*

**Math**

1 and 2 3 is false, since √2.25 = 1.5 is a radical that is not a whole number, but is not irrational
*July 9, 2015*

**Math**

whole natural excludes zero integers include negatives rational includes integers and fractions
*July 9, 2015*

**Algebra**

By the way, 2x^3 sqrt(10/x) is also correct. So, good work, I think.
*July 9, 2015*

**Algebra**

If you'll allow one more step, 2x^2 sqrt(10x)
*July 9, 2015*

**math**

If the committee is really 3 men, then Mary can't be on it at all. I suspect you meant 3 people. In that case, if either John or Mary is on the committee, then there are only 13 other people to pick for the other two seats. That gives us Committees with John: 13P2 = 156 ...
*July 9, 2015*

**math**

100-999
*July 9, 2015*

**Mathematics**

So, did you actually check your answer? tx=180 means ty=144 So, total time for X is 180+80=260 total time for Y is 144+80 = 224 distance from A of X to meeting place is L/260*80 distance from B of Y to meeting place is L/224*80 Add those up and you do not get L. Your mistake ...
*July 9, 2015*

**Physics**

work = force * distance, so assuming European conventions, where the ground floor is floor zero, work = 60*9.8*10 * 3*12 Joules power = work/time, so p = work/12 Watts
*July 9, 2015*

**Math**

70+W <= 150
*July 9, 2015*

**Algebra**

Since time=distance/speed, if his speed is s and the current's is c, then 15/(s+c) = 15/(s-c)-5 15/(2s+c) = 15/(2s-c)-1 Now just solve for s and c.
*July 9, 2015*

**mathematics**

I think you mean she sold 16 boxes, since she only had three different types. t+h+c = 16 40t+50h+60c = 800 That's not enough to completely specify a solution, but it will get you to t = c h = 2(8-c) So, clearly c<=8. If we start listing the possibilities, we get c,t h 8...
*July 9, 2015*

**math**

a) the shortest sides are in the ratio 8/3 b) so are the perimeters.
*July 9, 2015*

**math**

just multiply 13 by 21/15, the scaling ratio.
*July 9, 2015*

**Physics**

since a = 2.7 m/s^2, at t=4.2, v=11.34m/s Then its acceleration drops to (13.0-11.34)/5 = 0.332 m/s^2 So, starting at t=4.2, x = -108 + 0.332t + 0.166 t^2 At 5.7s after the first phase, then x = -100.7
*July 9, 2015*

**math**

what should be added to 4 to get 6? 6-4, or 2. Same here. you need to add (-2/15) - (2/3 + 3/5) So, use the common denominator of 15 to work with the fractions.
*July 8, 2015*

**math**

The common denominator is 63, so you have 54/63 - 126/63 - 49/63 + 57/63 ...
*July 8, 2015*

**maths**

Not much to this one. 1/10 = 7/70 ...
*July 8, 2015*

**maths**

I'll assume you meant 1/(x+1)+1/(x+2)= 2/(x+10) Putting all over a common denominator, the numerator becomes (x+2)(x+10) + (x+1)(x+10) = 2(x+1)(x+2) 2x^2+23x+30 = 2x^2+6x+4 I expect you can take it from there, eh? Just beware spurious roots that might make any of the ...
*July 8, 2015*

**Physics**

the only equation you really need is d=vt, or t=d/v. That gives you 114t = 79t+36 35t=36 t = 36/35 That's how long it takes B to overtake A. In that time, A travels 79*36/35 = 81.26 km You can think of this another way by noting that B is traveling 35 km/hr faster than A. ...
*July 8, 2015*

**algebra 1**

-72-4x^2+8x^3-36x Geez, have you never noticed that polynomials are generally written in descending powers? Much preferred would be 8x^3-4x^2-36x-72 Using synthetic division, this is easy, or you can visit calc101.com, click on the long division button and then enter your ...
*July 8, 2015*

**math (algebra)**

If x passed, then the rest (36-x) failed. So, adding up all the grades, we have 78x + 60(36-x) = 71*36 This is just a mixture problem in other guise.
*July 8, 2015*

**Math**

6720/56 = 120 So, you have nPr = nCr * 5! That means that r=5. Review the definitions of nPr and nCr to see why this is so.
*July 8, 2015*

**Calculus**

I first thought of x^2+1, but f(-1) = 2. So, next, 2x^2+1 f(x) = x^2+1 for x in (-5,-1)U(-1,1) 3 for x = -1 2 for x > 1 I think this fits the bill.
*July 8, 2015*

**math (algebra)**

or, note that x^32-1 = (x^16+1)(x^16-1) = (x^16+1)(x^8+1)(x^8-1) ... and if you keep expanding the differences of squares, you wind up with (x-1) at the end.
*July 8, 2015*

**Calculus**

for the 2nd part, if a function is differentiable, it is continuous. Hence it has a limit at every point.
*July 8, 2015*

**math**

clearly on the nth day you win 5^n dollars. So, what's 5^11? Send me my 10% commission check, ok?
*July 8, 2015*

**algebra**

it takes t seconds to fall 125 ft, where -16t^2 = -15 Now, the velocity is just -32t. or, in one operation, -32√(15/16)
*July 8, 2015*

**Computer Programming**

odd - you know how to do multiplication. Do a division in the same way. Just copy the multiply routine, and replace * with /. Be sure to watch out for division by zero.
*July 8, 2015*

**Computer Programming**

looks pretty good so far. But your best help is your IDE, or the javac error messages. If there are no compile errors, then just run your code and see what it produces. It looks like you are getting a handle on things. Just keep poking around to find code snippets that do what...
*July 8, 2015*

**algebra 2**

you want the total area, less the pool, to be 105. So, that means that the border has width x, where (6+2x)(10+2x)-(6)(10) = 105 x = 5/2 ft or 2'6"
*July 8, 2015*

**algebra**

There are 7 octaves, plus an extra A,B,C A) Since there are 8 A keys, there are 8C5=56 ways to pick them. For the G keys, there are only 7C5 = 21 choices. For any key, consider it like this. Pick a key from the 1st octave. Now there are fewer octaves to pick the other 4 keys. ...
*July 8, 2015*

**science**

recall F=ma? m = F/a now just divide.
*July 8, 2015*

**Maths**

Good work, but you had to use a different function. Poorly set problem...
*July 8, 2015*

**Calculus**

If you got a single value for an interval, it doesn't look good for the kid. y = 4x-6arctan(x) y' = 4 - 6/(x^2+1) = (4x^2-1)/(x^2+1) y" = 12x/(1+x^2)^2 You are correct with what you got. But, what do you have when y" = 0? An inflection point. That's where...
*July 7, 2015*

**Maths**

(1+x)^(1/5) = 1^(1/5) + (1/5)/1! x + (1/5)(-4/5)/2! x^2 + (1/5)(-4/5)(-9/5)/3! x^3 = 1 + x/5 - 2x^2/25 + 6x^3/125 Using the series, we have a problem. It only converges when |x| < 1. I think what you really want to do is find (x-1)^(1/5), using x=32. Then you have x^(1/5...
*July 7, 2015*

**Maths**

if x ml of 100% alcohol are added, then you want .15(400) + 1.00x = .32(400+x)
*July 7, 2015*

**Triginometry**

Metro: 45tan56° Gammapro: 45(tan56°+tan24°) It always helps in these problems to draw a diagram. Then you can see which sides of the triangle you have, and so which trig functions to use. Of course, it also helps to review your trig functions, and study the similar...
*July 7, 2015*

**Math**

again, use tan. he adjacent leg in each case is 7.4 be sure to add 1.8 to the answers, since that's how high the observation point is.
*July 7, 2015*

**Math**

the height is just 25(tan33°+tan55°)
*July 7, 2015*

**math**

1st, plot the point (1,-3) Now, a slope of -1 means that every time x changes by +1, y changes by -1. Starting at the point (1,-3), move right 1 and down 1 to (2,-4) and plot that point. Then draw a line through the two points. And review the concept of slope...
*July 7, 2015*

**Chemistry**

well, clearly, each mole of Mg produces one mole of MgO.
*July 7, 2015*

**math**

s = j-4 j+5 = 2s Now go for it.
*July 7, 2015*

**algebra**

If Wendy's speed is w, their combined speed of approach is 2w+4 Since time = distance/speed, and they meet after 4 hours, 120/(2w+4) = 4
*July 7, 2015*

**Math (Finite)**

A: y = .60 + .02x B: y = .045x I guess you can take it from there, eh?
*July 7, 2015*

**Algebra (Normal Distribution)**

8 is 2 std below the mean 16 is 4 std above the mean P(Z>4) = .9772 P(Z>8) = .0227 P(4<Z<8) = .9772-.0228 = .9545 You can play around with this stuff at http://davidmlane.com/hyperstat/z_table.html
*July 7, 2015*

**Maths**

bounce height 1: 80 * 3/4 = 80(3/4)^1 2: 80 * 3/4 * 3/4 = 80(3/4)^2 ...
*July 7, 2015*

**Algebra/ Pre Calc - eh?**

is there a question somewhere in there? You can start off by noting that √(78.5/π) ≈ 5
*July 7, 2015*

**Algebra/Pre Calc**

If you park n cars for t hours, car 1: x = 3 + 2(t-1) others: 3/4 that amount, or 3/4 (n-1)*x So, the total amount will be f(n,t) = (3+2(t-1))(1 + (3/4)(n-1)) = (3n+1)(2t+1)/4 So, 3 cars for t hours is f(3,t) = 5/2 (2t+1) So, let's check, say, f(3,4)=45/2=$22.50 1st car: 3...
*July 7, 2015*

**Math**

Fill in the tens place, and then start reading what they tell you. xxx7x xx37x 9x37x 9437x 94379
*July 7, 2015*

**Ucc**

12,48,82,19,66
*July 7, 2015*

**Not much of an Equation**

Hmmm.
*July 7, 2015*

**math**

5 digit greater 60000 6xxxx My ones digit is less than my 10000 digit 6xxx{0,1,2,3,4,5} on my other digit are the same This is where I get lost.
*July 7, 2015*

**phakamani secondary school**

talk to your school counselor.
*July 7, 2015*

**Math Statistics**

virtually zero. since there is no replacement between draws, 1st # 1/58 2nd # 1/57 ... and so on multiply them all together
*July 7, 2015*

**Grammar**

1 is 2 is 3 are 4 were 5 have become If these trouble you, you need to review the forms of the verb "to be"
*July 7, 2015*

**math**

well, 515% is not 3/10 515% = 5.15 = 5 15/100 = 5 3/20 or 103/20 Not sure what you want to do with the 3/10. If your typo meant +, then just note that 3/10 = 6/20.
*July 6, 2015*

**math**

375/200 = (15*25)/(8*25) = 15/8
*July 6, 2015*

**Math (Finite)**

multiply the 2nd row of A by the 2nd column of B: (2)(-2)+(3)(6) = 14 Verify at http://www.wolframalpha.com/input/?i={{1%2C4}%2C{2%2C3}}*{{3%2C-2}%2C{4%2C6}}
*July 6, 2015*

**physics 20**

The first question makes little sense, but the second can be answered by solving 13s = 7.25s+350 s = 60.87 Since Jack has to stop after only 60 seconds, he'll watch Zeke's heels as he escapes. One more second and he'd have had zebra for lunch.
*July 6, 2015*

**Calculus**

assume all logs are base 3. We have log x^2 = 2log4 - 4log5 log x^2 = log16 - log625 x^2 = 16/625 x = ±4/25 Yes, the -4/25 is a solution, since only x^2 appears, so it's always positive.
*July 6, 2015*

**Physics**

speed: y' = 3.12t+1.04 acceleration: y" = 3.12
*July 6, 2015*

**Physics**

75000km * 1000m/km * 1rev/.300*2π m = 3.98x10^7 rev
*July 6, 2015*

**Calculus**

v = ft/s dv/dt is thus ft/s^2 (acceleration) Since gravity is constant, v' is constant.
*July 6, 2015*

**Physics**

(a) 65.0 m/s * 1rev/.700π m = 29.557 rev/s
*July 6, 2015*

**math - eh?**

Does the pi1: mean something? That's my question. Do you have one?
*July 6, 2015*

**physics**

A. So, how far does sound travel in 6.16 seconds? That is the round trip, so the berg is half that far away. B. same problem in reverse. How long to make a round trip of 2*2.21 meters? distance = speed * time time = distance/speed
*July 6, 2015*

**F.g.c jos**

the faces of the cube are 28^2 So is the base of the pyramid. So, the composite volume is 28^3 + 1/3 * 28^2 * 16
*July 6, 2015*

**pre calculus**

we know that the fraction remaining after t years is f(t)=e^-(kt) for some k. So, find k: f(227) = e^(-227k) = 0.68 k = 0.001699 So, f(t) = e^(-.001699t) I expect you can take it from here, ok?
*July 6, 2015*

**Maths**

google is your friend. I searched for your question and found a solution at http://openstudy.com/updates/53803effe4b04df7f2086291 There are surely others, maybe not quite so complicated.
*July 6, 2015*

**math**

at the surface of the earth, g=9.8, so his weight would be 60*9.8 = 588 Newtons
*July 6, 2015*

**Physics**

I think you need to specify more. F=ma, but we don't know how long it took to reach its ballistic speed, so we have no idea of the initial acceleration.
*July 6, 2015*

**Science**

man, never heard of google, or online dictionaries?
*July 6, 2015*

**Science**

neither. Galileo figured that out.
*July 6, 2015*

**Math**

Or, you can work it from the other side, which I find easier at the start: x + 2x-40 = 150 3x = 190 x = 63.33 2x-40 = 126.67-40 = 86.67
*July 6, 2015*

**Science**

first, that's stationary, since the rock is presumably not made of paper. How long does it take the glass to fall 1.5 meters? Then figure the horizontal speed using speed = distance/time.
*July 6, 2015*

**physics**

of course, the air does not have constant density, but under the given assumptions, you want to convert pressure to meters: 1 pa = 1N/m^2 1.04*10^5 N/m^2 * 1m^3/1.3kg * 1kg/9.8N = 8163m or 8.163km The folks who have climbed Mt. Everest (7855m) would be interested to know this...
*July 6, 2015*

**Math**

Just review the derivation of arc length in 3 dimensions, as at http://tutorial.math.lamar.edu/Classes/CalcIII/VectorArcLength.aspx s = ∫√(f'^2 + g'^2 + h'^2) dt So, for your problem, f' = √2 g' = e^t h' = -e^-t s = ∫[0,1]√...
*July 6, 2015*

**Sequence**

Clearly the sequence is not a geometric progression. It is just a sequence of squares. I think that should get you going.
*July 6, 2015*

**math - eh?**

There is no way to tell. The combined ages of the children in no way tells you how many children there are. It does provide an upper limit though, assuming each child is at least 1 year old. Not only that, but the system of equations using the given conditions has no solution...
*July 6, 2015*

**Math**

Surely you can play around with the digits on this. For example, (1) Assuming no leading zero, that would be 1023456789 (4) The smallest number greater than 4316. That would be 4317. Are there really any that cause you difficulty? We can check your answers.
*July 6, 2015*

**mathematics :integration**

well, just use Reiny's solution, plugging in 5 where he used 0 for S.
*July 6, 2015*

**maths**

The product of all three roots is -c. So, if one root is -1, the other two must have a product of c. Hmmm. Not what you wanted. So, divide by x+1, and you have x^3 + ax^2 + bx + c = (x+1)(x^2 + (a-1)x + (b-a+1)) So, the other two roots must have a product of b-a+1. Also, of ...
*July 6, 2015*

**maths**

more than 3. f(x) = a(x+2)(x-5) will have those two zeroes. But a can have any value you like. Also, f may have higher degree than 2, since a(x+2)(x-5)*p(x) will also have those two roots, and p(x) can be any polynomial you like.
*July 6, 2015*

**Science**

The formula requires c^2 to preserve the units. c is velocity, measured in m/s energy E is measured in Joules, which are Force * distance. Force is mass * acceleration. So, E = (kg)(m/s^2)(m) = kg*(m/s)^2 = Mc^2 For the derivation, just read any introduction to special ...
*July 6, 2015*

**Physics**

You know that the max height is reached at v^2/2g sin^2θ, and the range is v^2/g sin2θ So, v^2/19.6 sin^2 θ = 2.96 v^2/4.9 sinθ cosθ = 29 Dividing that, we have tanθ = 0.408 θ = 22.2° v = 20.15 m/s So, the y-component of v is v sinθ...
*July 5, 2015*

**math**

if there is $x at 7%, the rest (8000-x) is at 9%. So, add up the interest: .07x + .09(8000-x) = 600 Now just find x and 8000-x
*July 5, 2015*

**Math**

the slope of 2x-4y-1=0 is 1/2 So, the slope if its perpendicular is -2 Now use the point-slope form to write the line through (2,1) with slope -2: y-1 = -2(x-2)
*July 5, 2015*

**math**

I get 5.94%, but you are correct. Bogus answer key.
*July 5, 2015*

**Calculus**

You are indeed wrong. Here is the graph of y: http://www.wolframalpha.com/input/?i=t^3+-+12t+%2B+3 You can see that y is decreasing for t between 0 and 2.
*July 5, 2015*

**Calculus**

I'll assume you meant y = t^3 - 12t + 3 the particle is moving downward when y is decreasing; that means y' < 0 y' = 3y^2-12 y' < 0 when 3y^2 < 12, or |y| < 2 So, since t>=0, y is decreasing when 0 <= y < 2. upward when y > 2 So, you are...
*July 5, 2015*