Saturday

August 1, 2015

August 1, 2015

Total # Posts: 32,558

**Maths**

one liter is 1000 cm^3 Since the base has an area of 50cm^2, it takes 50cm^3 to cover it to a depth of 1 cm. So, at 12000cm^3/min, the water level is rising at (12000cm^3/min)/50cm^2 = 240cm/min
*July 14, 2015*

**Algebra**

since 20% less effective each hour, that means that its effectiveness is 80% as much, and that repeats every hour. So, after x hours, the effectiveness is y = 0.8^x So, yes, it is exponential, and yes, it is decay. For B, since the initial dose is 200 mg, the amount left after...
*July 13, 2015*

**Math**

x/2 = 9th graders, leaving x/2 x/2 * 1/4 = x/8 = 8th graders, leaving x/2*3/4 = 3x/8 1/5 * 3x/8 = 7th graders, leaving 4/5*3x/8=3x/10 3x/10=12 = 6th graders. So, the team has 40 members. 20 9th graders 5 8th graders 3 7th graders 12 6th graders
*July 13, 2015*

**math - eh?**

I don't get it either. What comes after the equal sign?
*July 13, 2015*

**math**

just expand each product, and see whether all the terms are divisible by 6. For example, (2n+3)(3n+2) = 6n^2+13n+6 You can see that 13n is not necessarily divisible by 6. If you expand the others, you will see that one of them has all its terms multiples of 6.
*July 13, 2015*

**math**

The 1995th integer is 1994 more than the first one. so, x+1995+1994
*July 13, 2015*

**math**

q+n = 26 25q+5n = 10*1 + 16*10 25(26-n)+5n = 170 I expect you can take it from there, right?
*July 13, 2015*

**Math**

just put the words into symbols: B = 6 L = 2B T-B = L-T now start substituting B=6, so L=12 T-6 = L-T Now we know that L=12, so T-6 = 12-T 2T = 18 T = 9
*July 13, 2015*

**computers (hacking)**

google is your friend. I think you will find that (A) is what you want.
*July 13, 2015*

**french**

Just for starters, subjunctive is a mood, and infinitive is not. I expect you mean indicative. Just from my knowledge of Portuguese, I figure that 1 and 3 are indicative, and 2 is subjunctive. But, as Ms Sue says, our French expert will be glad to give feedback on your thoughts.
*July 13, 2015*

**Geometry**

If you draw a diagram, you can see that the apothem is just the altitude of a 30-60-90 right triangle with one side s/2. Recall that the sides of such a triangle are in the ratio 1:√3:2
*July 13, 2015*

**Problem solving (point of intersection)**

A: y=10x+40 B: y=20x
*July 13, 2015*

**Chemistry**

I'd say it is still nitrogen gas.
*July 13, 2015*

**ENGLISH**

The whole point of writing is communication. Improper spelling, grammar or punctuation makes it difficult or even impossible to understand. The person doing the writing has the responsibility to be clear. Do not make the reader struggle to figure out "what you mean."...
*July 13, 2015*

**math**

The two numbers are 70m and 70n, where m and n have no common factors. (70m)(70n) = 4900mn = 49000 = 4900*10 Thus, mn=10. So, m and n are 2 and 5, or 1 and 10.
*July 13, 2015*

**Math**

Think back on your days of learning multiplication, where if you are multiplying by a 3-digit number, you write down the partial answers, each row shifted over by one from the row above. That's all this is. We work with a base-10 system, so multiplying by a power of 10 ...
*July 13, 2015*

**the ultimate run-on sentence**

Why don't you repost it the way you received it?
*July 13, 2015*

**algebra**

There is a fixed cost. So, even if no bikes are produced, C(0) = 8000 Each bike costs 800 to make. So, for x bikes, that would be 800x. That means C(x) = 8000+800x How the heck did you arrive at f(x)=4800? That's a constant function. And who asked for f(x) anyway? We ...
*July 12, 2015*

**Math**

well, the vertex is at t = -b/2a = 72/32 = 9/4 So, find s(9/4)
*July 12, 2015*

**math**

well, it's a square with side=1 . . .
*July 12, 2015*

**math**

one of the factors will be (x-50). What is that when x=50?
*July 12, 2015*

**math**

You have to remember that (a-b)(a+b) = a^2-b^2 You have a denominator of x+√7 So, if you multiply top and bottom by x-√7, you have 2√7 (x-√7) --------------------- (x+√7)(x-√7) 2√7 x - 2√7√7 -------------------- (x)^2 - (&#...
*July 12, 2015*

**GREATER TOMMOROW**

a+ar = 6 ar^4 + ar^7 = 288 a(1+r) = 6 ar^4(1+r^3) = 288 1+r^3 = (1+r)(1-r+r^2), so r^4 * a(1+r)(1-r+r^2) = 288 6r^4(1-r+r^2) = 288 r^4(1-r+r^2) = 48 We probably want r an integer, so try to see what factors we have of 48 48 = 1*48 48 = 16*3 - bingo r = 2 so, a = 2 The sequence...
*July 12, 2015*

**Calculus**

g'(x) ≈ ∆g/∆x = [g(x+h)-g(x)]/h So, just pick a small h, and figure [g(π/2 + h)-g(π/2)]/h = [cos(π/2 + h)-cos(π/2)]/h = [(cos(π/2)cos(h) - sin(π/2)sin(h)-cos(π/2)]/h = -sin(h)/h So, pick any value of h close to zero, and...
*July 12, 2015*

**math**

In both cases, the slope is -5/8, so either the lines are identical, or they are parallel. Pick a point on one line, and see whether it is also on the other line. If y=0, then for line 1, x = -1 for line 2, x = -14 So, the lines do not intersect.
*July 12, 2015*

**Physics**

According to your formula, I get ∆T = ∆L/L * K I assume that the coefficient is set up to produce °C or °K (which are really the same thing). ∆T = (.0734cm)/(50cm) * (1.9x10^-5) = 2.789x10^-8 Now, somehow that does not seem right. That would mean that...
*July 12, 2015*

**math**

d = p-2 d = 3x p-2 = 3x p = 3x+2 So, after 10 seconds, Lee has run 10x meters Pat has run 10(3x+2) = 30x+20 So, Pat is 20x+20 meters ahead of Lee
*July 12, 2015*

**math**

recall how to factor the sum of two cubes ...
*July 12, 2015*

**math**

None -- two odd numbers always have an even sum.
*July 12, 2015*

**mathematics**

s+6 = 2(a+6) a+s = 42 Sena is 30
*July 12, 2015*

**Physics**

I guess that depends on what he wants to happen.
*July 12, 2015*

**mathematics**

see the answer given to taiwo below. Double it.
*July 12, 2015*

**math**

stop wasting our time with these stupid lottery questions.
*July 12, 2015*

**math**

or, try this to start out x+y = 2tan x-y = 2sin x^2-y^2 = (x+y)(x-y) = 4tan sin = 4sin^2/cos Saves having to expand those pesky squared binomials.
*July 12, 2015*

**math - take 2**

Looks like I used some different angles last time. I hope both methods produce the same answer!!
*July 11, 2015*

**math**

This one takes some drawing. Let's label the near lighthouse A, and the far one B. The ship began at P, and ended up at Q. It helps to draw a line due north from Q. A bit of analysis shows that PQ = 20 mi ∠BPQ = 95° ∠PBQ = 30° We want the distance QB, ...
*July 11, 2015*

**Algebra**

well, geez. Plug in t=8 and do the, uh, math!
*July 11, 2015*

**math**

just a little nudge can usually help.
*July 11, 2015*

**math**

x = y-8 2y = 4x Now do a little substitution for y, and you can easily find x.
*July 11, 2015*

**math circle geometrics**

draw a radius perpendicular to the chord. If the center of the circle is O, the chord is AB, and the midpoint of the chord is P, then you have a right triangle where the leg OP is 5, and the hypotenuse (the radius) is 7. So, PA=PB is half the chord length.
*July 11, 2015*

**math probability**

answered in a related question below.
*July 11, 2015*

**physics**

the x-velocity is 43.4/1.8 = 24.111 m/s so, the ball is hit at an angle θ such that cosθ = 24.111/26, so θ = 21.97° So, the y-velocity is 26sin21.97° = 9.73 m/s. The height of the ball is y = 9.73t - 4.9t^2 So, when caught after 1.8 seconds, y(1.8) = 1.638
*July 11, 2015*

**MTH 156**

you know the perimeter is 2(length+width) So, f(1,8) = 2(1+8) = 2(9) = 18 and so on for the others. To produce an output of 16, all you need is two numbers that add up to 8.
*July 10, 2015*

**Math**

since (x^a)^b = x^(ab) (√3)^2 = 3 So, if √3 = 3^a, (3^a)^2 = 3^(2a) = 3^1 So, 2a=1 √3 = 3^(1/2) The nth root of x is x^(1/n)
*July 10, 2015*

**Maths**

Oops. The 4th term is C(6,3)
*July 10, 2015*

**Maths**

The (x^3)(1/x)^3 term will be constant. That is the 4th term of the expansion. So, what is C(6,4)?
*July 10, 2015*

**Math**

r = 2j+3 r-3 = 4(j-3) 2j+3-3=4j-12 j=6 in 10 years, Joe will be 16
*July 10, 2015*

**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*