Friday

September 19, 2014

September 19, 2014

Total # Posts: 25,088

**math**

3278164781246
*July 28, 2014*

**math**

9/180 = 0.05 = 5%
*July 28, 2014*

**chemistry**

32 days is 4 half-lives. So, the mass is reduced to 1/2^4 = 1/16 of 40mg, or 2.5mg
*July 28, 2014*

**Math**

so far so good. Now just solve for b and plug that into your formula. Then check that (-3,-8) satisfies the equation.
*July 28, 2014*

**Math**

plot the point. Since the slope is 2/3, go right 3 and up 2 and plot another point. Draw the line connecting the two points.
*July 28, 2014*

**physics**

the difference is 4.9µC. So, move half that, or 2.45µC. Now just convert that to no. electrons.
*July 28, 2014*

**math/help**

4 1/6 = 25/6 1 1/6 = 7/6 so, (25/6)/(7/6) = 25/7 3 3/1 ??? fix that and work it as in the above one.
*July 28, 2014*

**math**

just as usual. Where is y" positive? e^-3t is always positive, so all you need is 2t-3 > 0 t > 3/2 e^3/2 = 4.48, and you can see from the graph that it is concave upward for x > 4.48 http://www.wolframalpha.com/input/?i=plot+x+%3D+e^t%2C+y+%3D+te^-t+for+1%3C%3Dt%...
*July 28, 2014*

**math**

x = e^t y = te^-t dy/dx = y'/x' = (1-t)e^-t/e^t = (1-t)e^-2t d^2/dx^2 = (x'y"-x"y')/x'^3 = ((e^t)(t-2)e^-t - (e^t)(1-t)e^-t)/e^3t = (2t-3)e^-3t or, do it directly x = e^t, so y = lnx/x y' = (1-lnx)/x^2 = (1-t)e^-2t y" = (2lnx-3)/x^3 = (2t...
*July 28, 2014*

**Science**

why do you include a third dimension? The taxi cannot travel vertically. The total displacements are 20+6=26 blocks south 15 blocks east. So, √(15^2+26^2) = √901 = 30.0
*July 28, 2014*

**physics**

15.7 + 17.5
*July 28, 2014*

**math**

1/2 * 1/2 * 1/6
*July 28, 2014*

**Algebra**

Start by expanding the parentheses: 3(x-1) -2(x^2+3x+4)-5(x+9) 3x - 3 - 2x^2 - 6x - 8 - 5x - 45 Then collect terms of like degree: -2x^2 + (3-6-5)x + (-3-8-45) -2x^2 - 8x - 56
*July 27, 2014*

**Math**

If their heights are k and r, then k/375 = sin 32° r/375 = sin 38° So, the difference is r-k = 375(sin38°-sin32°)
*July 27, 2014*

**math**

that's because you mixed up dollars and cents. It asked for only dollars.
*July 27, 2014*

**math**

3:40 to 6:20 is just 2 hours and 40 minutes. That should get you going.
*July 27, 2014*

**Math**

Assuming you mean "I" and not "O", just pick any two values for x and calculate the y: x=0: y=4 x=4: y=5 So, the points (0,4) and (4,5) are on the line. Plot them, and draw a line between the two points.
*July 27, 2014*

**math**

There are only 3 colors. Any group of more than 3 cards will have to have a duplicate color.
*July 27, 2014*

**Statistics**

0.066-0.033 < p < 0.066+0.033
*July 27, 2014*

**english**

That "ing" is a big clue for a gerund.
*July 27, 2014*

**chemistry**

when you say it was immersed, that implies there was some other liquid in the cylinder. If all you mean is that the sodium exactly filled the cylinder, then the density is obviously 405.5g/32.5ml = 405.5/32.5 g/ml
*July 27, 2014*

**Chemisrt**

What you have is just D = D0*x where x is all that exponential stuff. So, D0 = D/x Of course, R is not specified. If it's R you are looking for, then just work it out like this: exp[-Ea/R*T] = D/D0 -Ea/R*T = ln(D/D0) R = -Ea*T/ln(D/D0)
*July 27, 2014*

**maths**

if you mark off a length of 4, you can easily construct a length of 30. Double the 4 to 8, double the 8 to 16, double the 16 to 32. Halve the 4 to get 2, and subtract that from the 32. Now construct the leg BC, and the right angle at C. Then mark off a circle of radius 30 to ...
*July 27, 2014*

**algebra**

take a look at http://www.jiskha.com/display.cgi?id=1406381756
*July 27, 2014*

**math**

just plug in the values and see. For example, take (1,-2). Is 3*1 + 3*1 - 6 < -2 ? 0 < -2 ? No. Now try the others.
*July 27, 2014*

**math**

if you can recognize a quadratic and an inequality (as opposed to an equation), you should have no trouble picking the correct choice.
*July 27, 2014*

**math**

2(w+1.2w) = 88 4.4w = 88 w = 20 so, area = 20(1.2*20) = 480
*July 27, 2014*

**calculus 2**

dy/dx = y'/x' = (-3sint)/(2cost) = -3/2 tan t d^2y/dx^2 = (x'y"-x"y')/x'^3 = ((2cost)(-3cost) - (-2sint)(-3sint))/(8cos^3 t) = -3/4 sec^3 t Check: y = 3/2 √(4-x^2) y' = -3/2 x/√(4-x^2) y" = -6/(4-x^2)3/2 I'll leave it to ...
*July 26, 2014*

**calculus 2**

I think she means y = ∛x
*July 26, 2014*

**Math**

Correct. So, 5/11 - 7/11 = -2/11
*July 26, 2014*

**Math**

you're working with 11ths. So, what's 5-7?
*July 26, 2014*

**math**

s = ∫[0,6π] √((dx/dt)^2 + (dy/dt)^2) dt = ∫[0,6π] √((1-2cost)^2 + (2sint)^2) dt = ∫[0,6π] √(1-4cost+4cos^2t + 4sin^2t) dt = ∫[0,6π] √(5-4cost) dt
*July 26, 2014*

**trigonometry**

15rev/12sec = 5/4 rev/sec = 5π/2 rad/s That's the speed of the smaller pulley Assuming they are both attached to the same belt, the larger pulley's rotational speed is 6/20 the speed of the smaller one.
*July 26, 2014*

**Math - trig**

no, no. It's just a quadratic equation, in cosx, rather than just x using the quadratic formula, we have cosx = (1±√3)/4 or, -0.183, 0.683 So, just find the angles with those values as cosine.
*July 26, 2014*

**math**

the price, for n >= 150, is p(n) = 200-n Revenue is price*quantity, so r(n) = n(200-n) = 200n-n^2 That's just a parabola. The vertex is the point of maximum revenue. That's just algebra I, so no sweat. . . . right?
*July 26, 2014*

**math**

Looks like (a) to me. Just use the quadratic formula.
*July 26, 2014*

**trig**

draw a right triangle with the tops of the poles as the ends of the hypotenuse, and the bottom side perpendicular to the poles. You have a 5-12-13 triangle. It is useful to learn some of the basic triangles with integer sides -- they pop up frequently. 3-4-5 5-12-13 8-15-17 7-...
*July 26, 2014*

**College Algebra**

All you need is f(-1)*g(-1) = 4 f(x) = 2 g(x) = 2 will work, but they are rather trivial. I'm sure you can come up with two functions that work.
*July 25, 2014*

**Algebra**

Clearly E cannot exceed 5, since even with borrowing, A cannot exceed 10. That would mean something like FL50 -B55 ------- MO95
*July 25, 2014*

**Algebra**

1/3 of the mice are female, so 1/6 of the mice are white female 1/6 of the mice are brown female 3/5 are brown, so 3/5-1/6 = 13/30 are white male 1-(1/3+13/30) = 7/30 are brown male So, brownmale/whitemale = 7/13
*July 25, 2014*

**MATH WORD PROBLEMS**

to be centered, the extra space must be divided into two equal parts.
*July 25, 2014*

**College Algebra**

q(x) = 73(x+1)^2+2 h(x) = x^2 g(x) = (x-1)(x-2)(x-3) Since x^0=1 for any x, we have s(x) = 2*a^(kx) for some a and k. 2*1/2 = 1, so s(x) = 2*4^(-x/2) r(x) will involve something/(x-3) x-2 is zero at x=2, so r(x) = (x-2)/(x-3) will work
*July 25, 2014*

**College Algebra**

reflected: -|x| stretch vertically: -4|x| shifted: -4|x+3| see http://www.wolframalpha.com/input/?i=plot+y%3D|x|%2C+y%3D-4|x%2B3| You want t where 1(1+.075/4)^(4t) = 7200 The rule of 72 indicates it should double about every 10 years. Since 7200 is about 2^13, I expect it will...
*July 25, 2014*

**Sinusoidal! - Missing Data!!**

Clearly, the radius of the wheel is 9.98, or, due to the careful engineering of the triangle, call it 10 meters. So, the height, starting at the bottom, will be h = 11-10cos(kt) So, we just need to find k. The vertex angle of the triangle satisfies sin θ/2 = 9.23/14.35 so...
*July 25, 2014*

**math**

one hitch is that there are only 3 ballads. Anyway, peter, fix that and redo Reiny's calculations to find that x=5. As for my hint, since there must be 12 songs in all, the missing x pieces must total 5.
*July 24, 2014*

**math**

since there are 3 ballads, and 1/4 of the total are ballads, there must be 12 songs in all. That help?
*July 24, 2014*

**math**

Since the sides are equal, and the hexagon has twice as many sides as the triangle, ...
*July 24, 2014*

**Math 221**

fix the typo. Surely you can find the slope of the line. The parallel line has the same slope -- call it m. Then, recall the point-slope form of a line with slope m that passes through the point (h,k): y-k = m(x-h)
*July 24, 2014*

**College Algebra**

it doesn't matter what value g(2) is, because f(x)=7 whatever x is. On a bit more realistic note, you can dream up lots of scenarios. Looking at exponential stuff, for instance, suppose f(0) = 7. So, we could say f(x) = 2x^2+9x+7 Then, all we need is some g(x) such that g(...
*July 24, 2014*

**College Algebra**

f(x) = 7 g(x) = whatever you want. Maybe a bit more specific constraints?
*July 24, 2014*

**bean**

875 = 25 * 35 So, you need to draw a rectangle which contains 35 squares. That should help.
*July 24, 2014*

**calculus**

for intercepts, set x=0 and evaluate y for the y-intercept Set y=0 and solve for x to get the x-intercepts. Note that g(x) = x(x-3)^2 p(x) = x^3(x-4) Max/min occurs when 1st derivative = 0. No problems there, right? But is it a max or a min? If the curve is concave up, it'...
*July 24, 2014*

**Algebra2**

since T4 = T2 * r^2, 6r^2 = 54 So r=3 (or, r = -3)
*July 24, 2014*

**Alegbra**

y=0
*July 24, 2014*

**math**

if she had s savings, then after spending 1/3 of it, she had 2/3 s left. So, 2/3 s = 780
*July 24, 2014*

**math**

as with all fractions, clear things out by multiplying by the denominator So, multiply by a and you have a^2 = 1 done
*July 24, 2014*

**math**

Is the smaller circle inside the larger one? If so, do they share a center? Do they touch? If the two centers are more than 7 apart, then the distance between them can be anything.
*July 24, 2014*

**math**

Huh. I thought that f was the total ounces, f>b. So, the cost is cb+d(f-b)
*July 24, 2014*

**math**

looks like 9 gallons to me.
*July 24, 2014*

**physics**

just add the two momenta. The total will remain unchanged. 1.5*10^3 * 20 - 9.5*10^2 * 26 = -5.3*10^3 kg-m/s
*July 24, 2014*

**physics**

since the speed decreases at 10 m/s every second, v = 30 - 10t after t seconds. Looks like it takes 3 seconds to stop. The distance traveled in t seconds is thus s = 30t - 5t^2 You can use that to figure out (b) and (c)
*July 24, 2014*

**math**

all distances are multiplied by a factor of 3.
*July 24, 2014*

**Maths.literacy**

first step: discover the distance to be covered. Next, divide that by 185 to get the number of hours required.
*July 24, 2014*

**Maths**

If there are n tests already taken, we need 84n + 100 = 86(n+1) 84n + 100 = 86n + 86 2n = 14 n = 7
*July 23, 2014*

**math**

we have s/b = 3/5 s/a = 9/17 total unshaded area is a+b-s, and we want s/(a+b-s) we know that b = 5/3 s a = 17/9 s so, we have s/(a+b-s) = s/(5/3 s + 17/9 s - s) = s/(23/9 s) = 9/23
*July 23, 2014*

**Maths**

what do we know? (d+k+l)/3 = 42 d = 6+(k+l)/2 k = l+6 So, start substituting: d+l+6+l = 126 2d = 12+l+6+l or, d+2l = 120 2d-2l = 18 Add these to get 3d = 138 d = 46
*July 23, 2014*

**M**

if there are b bigs and s smalls, we have b+s = 16 1200b + 1500s = 21000 since s = 16-b, we have 1200b + 1500(16-b) = 21000 or, 12b + 15(16-b) = 210 12b + 240-15b = 210 3b = 30 b = 10
*July 23, 2014*

**Math**

357mi/21gal = 357/21 m i/gal = 17 mi/gal dr = 1/3 p lr = 2k k = 3/2 p - dr-lr-k = 3/2 p - p/3 - 2(3/2) - 3/2 = 3/2 p = 9
*July 23, 2014*

**math**

m * 1/2 * 1/3 = 1/6 m Use one envelope and a stamp to advertise for a new office manager!
*July 23, 2014*

**Math**

surely you can solve at least some of these exercises. At least the amplitude? Review the material about sinusoidal functions, and I think some of it will become clear. Recall that A sin(Bx) has amplitude A and period 2pi/B. Also, look at the graph of cos(x). It has a max at t...
*July 23, 2014*

**Alegbra**

surely you know that division by zero is undefined. For if x = 3/0, that means that x*0 = 3 There is no number you can multiply by zero and get anything other than zero!
*July 23, 2014*

**calculus**

assuming six digits, a,b,c,d,e,f, we have a = √b b = a^2 (well, duh) c+f = 14 c+d+e+f = d^2 a+b+c+d+e+f = 37 ae = d+e+f b+c+d = af Play around with that for a while.
*July 23, 2014*

**trigonometry**

one complete rotation moves the container a distance equal to the circumference of the winch spool. one complete rotation is 2pi radians. 5pi/6 radians is thus (5pi/6)/(2pi) = 5/12 of a complete rotation. the circumference is 2pi*6 = 12pi inches, so the container is lifted (5/...
*July 23, 2014*

**advance algebra**

If you mean synthetic division, the web site below shows all the details involved. http://www.mathportal.org/calculators/polynomials-solvers/synthetic-division-calculator.php
*July 23, 2014*

**maths**

the job takes 3*8*10=240 typist-hours. 2 typists working x hours per day perform 2x typist-hours per day. So, 2x*12 = 240 x = 10 hours per day
*July 23, 2014*

**Calculus**

I find it a bit easier not to expand the derivative f'(x) = 2x(4x-15)/(8x-15)^2 Clearly f'=0 when x is 0 or 15/4 So, f'(15/4)=0, and 3 < 15/4 < 5 f'(0)=0 also, but 0 is not in [3,5] The graph at http://www.wolframalpha.com/input/?i=x^2%2F%288x-15%29+for+3...
*July 22, 2014*

**calculus**

Sounds like they wanted f'(c) rather than c.
*July 22, 2014*

**math**

add 1 for each successive integer. So, what is y-3 + 1+1+1+1 ?
*July 22, 2014*

**Calculus**

Think of the graph for y = x^3 It has no max/min, but just an inflection point at x=0. You function is just the same, only stretched by 2, shifted left by 5, and shifted up by 7.
*July 22, 2014*

**math - bogus**

Two problems: (1) no value given for x (2) I suspect a typo, since there is no "x" term, and two constants.
*July 22, 2014*

**Geometry**

area of 3x3x3 cube is 6*9=54 area of 2x2x2 cube is 6*4=24 If not joined, total area is 78 The maximum concealed surface area is an entire face of the 2-cube, on both solids: 2*4 = 8 So, the minimum exposed area would be 78-8 = 70
*July 22, 2014*

**algebra**

3/5x is not defined for x=0 1 - 3/5 = 2/5 1 - 3/10 = 7/10 If you meant y = 1 - (3/5) x then just plug in the values: 1 - (3/5)(0) = 1 1 - (3/5)(1) = 2/5 1 - (3/5)(2) = -1/5
*July 22, 2014*

**Math**

I'd have to say 90 degrees. If the struck ball has some backward velocity, the striking ball would have to increase its forward speed to compensate.
*July 22, 2014*

**Math**

ACBD
*July 22, 2014*

**mathematics**

If there are x bundles, x/3 are morning 2 = afternoon That leaves 2x/3 - 2, of which x/3 - 1 are regional 1 is local 1 is out of state Add them up to get x/3 + 2 + x/3 - 1 + 1 + 1 = x 2x/3 +3 = x 3 = x/3 x = 9
*July 22, 2014*

**Math - thanks Reiny**

I guess I didn't read the question too carefully, and failed to answer it fully.
*July 22, 2014*

**Math**

look at the differences between successive terms: -1 -3 -5 -7 so, the next will be 15-9=6
*July 22, 2014*

**Math**

There are several standard right triangles with integer sides. It will help a lot if you just learn them -- they turn up often in problems, and it's nice not to have to do the calculations every time. 3-4-5 5-12-13 8-15-17 7-24-25 and multiples of those values
*July 22, 2014*

**Alegbra**

2•5^2•7
*July 22, 2014*

**advance algebra - oops**

Oops mixed up price and quantity p(x) = x(500-x)-35(500-x) = (x-35)(500-x) assuming no extra dolls are made...
*July 22, 2014*

**advance algebra**

profit = revenue - cost revenue = price * quantity. So, p(x) = x(500-x)-35x Now just plug in your data
*July 22, 2014*

**SECONDARY ALGEBRA**

nice try, but you're mixing things up. Why do you say 120 m^3? m^3 is volume, not are or length! And why multiply the perimeter by the length, anyway? Just take a step back and work things out. The area is length * width The 120m of fencing reaches around the field -- that...
*July 22, 2014*

**Math**

Just translate the words to algebra. Then solve. For example, #3: 3/8 of 768 = 288 5/6 are below senior, so 1/6 are seniors. 1/6 of 288 = 48 Where do you get stuck on the others?
*July 21, 2014*

**Calc**

If you mean f'(t) = -8 * 0.8^t, then f(t) = -8/ln(0.8) * 0.8^t + C since f(0) = 90, 90 = -8/ln(0.8) + C C = 90 + 8/ln(0.8) So, f(t) = -8/ln(0.8) * 0.8^t + 90 + 8/ln(0,8) = 90 + 8/ln(0.8) (1-0.8^t) = 90 - 35.85 (1-0.8^t) So, plug in t=10
*July 21, 2014*

**ENGLISH**

If you are looking for a complete sentence, What can he do? is the only option. The other phrases are all acceptable in various contexts.
*July 21, 2014*

**Math**

17(4+2*17) = ?
*July 21, 2014*

**math**

You can see some analysis here: http://www.wolframalpha.com/input/?i=sum+3%28-1%29^n%28n%29%28x^n%29 It will probably give you a start on proving the answer.
*July 21, 2014*

**algebra**

if the length is x, 2(3/4 x + x) = 100
*July 20, 2014*

**Math**

28' = 853.44 cm 18' = 548.64 cm Easy way, assuming partial pieces are tucked in as needed: (853*548)/(60*40) = 195 Now, you can do several kinds of approximation, requiring whole pieces, etc. One easy way is to round up the lawn area to multiples of 40 and 60: 853/60...
*July 20, 2014*

**physics**

just figure how much potential energy (mg ∆h) has been lost. That has been converted to kinetic energy.
*July 20, 2014*

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