Saturday

September 20, 2014

September 20, 2014

Total # Posts: 25,088

**Math**

20 cows 70 animals so, 20/70
*June 10, 2014*

**Math - incomplete**

Reiny went through this for you once. Now, maybe if you say which side of STU is b, we can make some headway.
*June 10, 2014*

**Algebra 1**

You did not factor correctly. x^2-4x+4 = (x-2)(x-2) If that's what you got, then you clearly don't understand what it means. x-2 = 0 when x=2, not -2.
*June 10, 2014*

**averages**

8(x+2) = 8x-24+y 8x+16 = 8x-24+y 40 = y It doesn't matter what the average age is. Replacing a 24-year-old by a 40-year-old adds 16 years to the total ages, raising the average by 2.
*June 10, 2014*

**physics**

72t + 1/2 at^2 = 70 72 + at = 54 so, a = -16.2 m/s^2 applied for t=10/9 seconds
*June 10, 2014*

**algebra**

since g(3) = 2, g^-1(2) = 3 since h(-4) = 1, h^-1(1) = -4 (h*h^-1)(-7) = h(7)*h^-1(-7) = (-5)*(-8) = 40 If you meant (h◦h^-1)(-7) then that would be -7, since by definition (h◦h^-1)(x) = x.
*June 10, 2014*

**Math**

y = 2cos(3x+135) cos(kx) has period 2pi/k, so y has period 2pi/3. The 135 is just a phase shift, and does not affect the period.
*June 10, 2014*

**check answer**

correct.
*June 9, 2014*

**Geometry**

since area grows as r^2, the area grows by (1/2)^2 = 1/4
*June 9, 2014*

**Goemetry**

PQ has length √(2^2+15^2) = √229 P'Q' has length 4 times that.
*June 9, 2014*

**math (check answer plz)**

Repeating an experiment naturally gives rise to experimental probability. Since no experiment is described, the probability must be theoretical only. So, (C).
*June 9, 2014*

**math**

the clue is that (x+3) divides the volume. So, a little checking shows that the volume v = (x+3)(x-7)(x+9) so, if x+3=15, x=12 and the box is 15x5x21
*June 9, 2014*

**math**

surely you have the formula for the period of a pendulum of length L (and small amplitude): T = 2π √(L/g) Now just plug in your numbers.
*June 9, 2014*

**Math**

-.05t + 300 = 182 Now just solve for t.
*June 9, 2014*

**Calculus**

we just did one of these x(t) = 3t^2 - 18t + c Now just figure x(6)-x(0)
*June 9, 2014*

**Maths**

The max occurs when x = -b/2a = 5/4, and is indeed 65/8 wolframalpha.com confirms this: http://www.wolframalpha.com/input/?i=-2x^2%2B5x%2B5
*June 9, 2014*

**Maths**

done earlier, and you were correct.
*June 9, 2014*

**Algebra**

m = miles g = gallons m = 20g
*June 9, 2014*

**math *check***

6 possible outcomes only 1 is a 5 So, theoretical P(5) = 1/6 You rolled 12 times, so that's B: experimentation. Evidently the die was heavily loaded.
*June 9, 2014*

**Math**

Correct. Reiny missed the -2x^2. Even experts trip over the details sometimes.
*June 9, 2014*

**Calculus**

Oops. Flipped a minus sign f(3) = 9-27+c = -18+c total change is thus -18
*June 9, 2014*

**Algebra**

just solve for x in 2771x/(100-x) = 36000 x = 92.85%
*June 9, 2014*

**Math**

Let the distance be d. If the kite is between the girls, d/sin75° = 20/sin40° But, if Kate is between the kite and Abigail, then d/sin25° = 20/sin40°
*June 9, 2014*

**equation**

after m months, you have 10*3^(m/2)
*June 9, 2014*

**Algebra**

0 < L <= 90 2L = 330-2W L = 115-W 0 < 115-W <= 90 90 >= W-115 > 0 205 >= W > 115
*June 9, 2014*

**Algebra**

(f-h)(4) = f(4)-h(4) = (2*4+5) - (7-4/3) = ?
*June 9, 2014*

**math foundations 20**

you want x such that P(Z<x) = 0.025 That means that x must be more than 1.96 std below the mean. In this case, that's 3.128 years.
*June 9, 2014*

**math**

C(12,2)*2 assuming the scoops must be different flavors. If duplicate scoops are allowed, then it's just 12^2 * 2
*June 9, 2014*

**Math**

You'll be covering rational functions, asymptotes, logarithms, inverse functions, and more. Go to your local used-book store, and buy a cheap text for Algebra II. Then, go for it -- with more tools at your disposal, the kinds of problems you can solve get much more ...
*June 8, 2014*

**Math 11**

If the marker is at distance x away from the spot just below the balloon, we have h/x = tan 27.8 (h+345)/x = tan 46.2 Eliminate x to get h/tan 27.8 = (h+345)/tan 46.2 Now just solve for h.
*June 8, 2014*

**math help plz2!!!!**

from the vertex, we know that y = a(x+3)^2+5 Now plug in the values to get a: 1 = a(-6+3)^2 + 5 9a = -4 a = -4/9 y = -4/9 (x+3)^2 + 5 See http://www.wolframalpha.com/input/?i=y+%3D+-4%2F9+%28x%2B3%29^2+%2B+5
*June 8, 2014*

**algebra**

we breathlessly await further developments.
*June 8, 2014*

**math**

as with all parabolas, the vertex (in this case a maximum) is at p = -b/2a = 150/.006
*June 8, 2014*

**Math**

as with all parabolas, the vertex (in this case a maximum) is at x = -b/2a = 80/0.0002
*June 8, 2014*

**MATH**

the length is 270-x So, the area is length*width, or f(x) = x(270-x) As with all parabolas, the vertex is midway between the roots, so in this case, it's at x=135. Since the graph opens downward, the vertex represents the maximum possible area.
*June 8, 2014*

**MATH**

from the values of the roots, we know that the functions will be of the form y = ax(x+4) So, pick a positive to open upward, and a negative to open downward. Any nonzero value will do.
*June 8, 2014*

**Calculus**

hit the ground == drop 400 ft. So, 16t^2 = 400 Now just solve for t.
*June 8, 2014*

**math**

7 filled 8 unfilled Choose 6 of each. So, C(7,6) * C(8,6) = ?
*June 8, 2014*

**Math**

If two weigh 51, that's the minimum for two boys, leaving the maximum for the 3rd boy of 3*159-2*51 = 159-102 = 57
*June 8, 2014*

**Calculus**

dv/dt = 0.6t cos(0.08t^2-1) v = 3/8 sin(0.08t^2-1) + c Since v(0) = 14, c = 14+3/8 sin(1) = 14.3 v(t) = .375 sin(.08t^2-1)+14.3 Now just evaluate v(10)
*June 8, 2014*

**Algebra/could show me how to work this problem**

I suspect a typo. Why not just say 2x^2+1? At any rate, assuming things are correct as written, for any input, just substitute it for all the x's and evaluate for the output. input: -2, output (-2)^2+(-2)^2+1 = 4+4+1 = 9
*June 8, 2014*

**Physics-can someone please check this**

(b) The horizontal speed is unaffected by gravity, so it remains 24.5 m/s. In 3 seconds, John travels 3*24.5 = 73.5 meters. (a) we know that the vertical position, starting at y0 is y(t) = y0 - 4.9t^2 Since y(3)=0, we can get the initial height by solving y0 - 4.9*9 = 0 y0 = ...
*June 8, 2014*

**Math**

wow. cubics are not generally easy to solve. Best bet is a graphical or numerical solution. wolframalpha gives http://www.wolframalpha.com/input/?i=4x^3-6.68E-7x^2%2B1.67E-8x-1.04E-10 The root is very close to zero, since the function is very nearly 4x^3=0 Blowing up the graph...
*June 8, 2014*

**math**

lose all the nonsense text. You have (x-1)^2 + (x-2)^2 + (x-3)^2 = 0 Now, you know that (x-1)^2 is a parabola, which is tangent to the x-axis at x=1, because of the double root. Similarly, the other two terms are never negative. So, since we are adding up three positive values...
*June 8, 2014*

**math**

you start out talking about two numbers, toss in some unknown quotient (maybe not even in lowest terms) then ask for "number"? The question is mighty unclear to me.
*June 8, 2014*

**Math**

just add .145258x to both sides and you have 1.145258x = .145258 now divide by 1.145258 and you get x = 0.126834
*June 8, 2014*

**Doppler Effect**

for non-relativistic speeds, we can use the approximation. c/520 = (1+v/c) * c/590 520(1+v/c) = 590 1+v/c = 59/52 v/c = 7/52 v = 7/52 c Is that relativistic? Generally, less than 0.1c is considered non-relativistic, so we may be a bit off, but if that matters, use the exact ...
*June 8, 2014*

**mathematics**

The only possible choice assumes a typo where you meant to say that one quarter of x is 36. Then, x is 144. Hmm. Unless the question reads 4 quarters of x is 36. What is 1 quarter of x? Then the answer is 9.
*June 8, 2014*

**science**

Assuming you meant 0.400g/dm^3, that translates to 0.0004 g/cm^3 So, 500cm^3 of that means 0.2 g Or, in one step, that's 500 cm^3 * (1dm/10cm)^3 * 0.4 g/dm^3
*June 8, 2014*

**physics**

The orbital period is given by T = 2π√(r^3/GM) We want M, which is thus M = r^3/G * (2π/T)^2 Now just plug in your numbers.
*June 7, 2014*

**Maths**

Looks to me like they could all be 8. Are there any restrictions on the values allowed? 2014 is not a multiple of 5, so there is no cycle of 5 numbers which repeats.
*June 7, 2014*

**Algebra/not sure what to do**

f(x) = x-8 for whatever value x has. So, if x=p, f(p) = p-8 Just replace x with the desired value throughout the entire line.
*June 7, 2014*

**math**

I'd say yes. That's what Accounts Receivable are for -- waiting for cash flow to be realized. That's assuming the invoice is not generated until a purchase is confirmed. But, what do I know? I may be off base here.
*June 7, 2014*

**Number Theory**

Since the n numbers are divided up in pairs, I'd say n/2 copies. Hence the formula for the sum: n(n+1)/2 Technically, that's [n+1]/2 where [] is the greatest-integer function.
*June 7, 2014*

**maths**

If P is x meters from the base of the pole of height h, then h/x = tan 53° h/(x+20) = tan 28° eliminate x and you have h cot 53° = h cot 28° - 20 h = 20/(cot28°-cot53°)
*June 7, 2014*

**math**

10(q+7) + 25q = 280
*June 7, 2014*

**Maths**

If there are x children, then .6x = 18 x = 30 78? 1? You just throwing darts at numbers? If not, show you r work, so we can help you get it right.
*June 7, 2014*

**math**

If we add up terms n through n+10, then we get (n+10)/2 (2a + (n+9)45) - (n-1)/2 (2a+(n-2)45) = 891 11a+495n = -1089 a+45n = -99 If we are adding up the first 11 terms, then a = -144 and T28 = -144+27*45 = 1071 T45 = -144+44*45 = 1836 But, if we add up terms T5 through T15, ...
*June 7, 2014*

**Calculus**

Looks good to me.
*June 7, 2014*

**Calculus**

x(t) = -cos t + c now you know that x(0) = 3, so plug in t=0 to find c. Then you can use t=2 to get x(2)
*June 7, 2014*

**Maths!**

300 = 100 + 40*5 So, set things up as an arithmetic sequence, and find that S41 = 41/2 (100+300) = 8200
*June 7, 2014*

**maths**

simple: 10000(1+.12*5) compound: 10000(1+.10)^5 evaluate and compare.
*June 7, 2014*

**calculus**

c(x) = 350 + .20 x
*June 7, 2014*

**Algebra**

are there any pairs with the same 1st element? If not, it is a function.
*June 7, 2014*

**math**

or, using de Moivre's rule, 1+i = √2 cis π/4 so √(1+i) = ∜2 cis π/8 1-i = √2 cis -π/4 so √(1-i) = ∜2 cis -π/8 √(1+i)/√(1-i) = cis π/4 Now the angle doesn't matter, since cos^2+sin^2 = 1
*June 6, 2014*

**math**

√(1+i)/√(1-i) = √(1+i)√(1-i) / (1-i) = √(1-i^2) / (1-i) = √2/(1-i) = √2(1+i) / (1-i)(1+i) = √2(1+i)/2 = 1/√2 + 1/√2 i a = 1/√2 b = 1/√2 a^2+b^2 = 1/2 + 1/2 = 1
*June 6, 2014*

**Math**

since the slopes are the same, the lines are parallel. Or, in this case, they are the exact same line.
*June 6, 2014*

**Math**

Or, knowing that the general circle is (x-h)^2 + (y-k)^2 = r^2 plug in your points to get (-5-h)^2 + k^2 = r^2 h^2 + (4-k)^2 = r^2 (2-h)^2 + (4-k)^2 = r^2 h = 1 k = -19/8 r^2 = 2665/64 and we have the circle as derived above The brute-force way, of course, is to plug your ...
*June 6, 2014*

**Math**

The center will lie at the intersection of the perpendicular bisectors of the line segments (chords) joining the points. If we label the points A,B,C, then The midpoint of AB is at (-5/2,2) The slope of the chord AB is 4/5 The line AB is y = 4/5 (x+5) The slope of the radius ...
*June 6, 2014*

**math**

-3 + i^2y = -3-y The conjugate of x^2+y + 4i is x^2+y -4i so, we want -3-y = x^2+y - 4i In no case is that ever true We can have -3-y = x^2+y, but there's no way to get the -4i I suspect a typo in the problem.
*June 6, 2014*

**Math**

#1. The kth odd number is 2k-1 Think about it : 1,3,5,... #2 It will be a multiple of 60. So, what's the biggest 3-digit multiple of 60? #3 There are 203 numbers from 101-303. Knock off one end, since both are odd, and half of the remaining 202 are even. #4 same thing #5 ...
*June 6, 2014*

**math**

2 3/4 = 2 + 3/4 1 1/4 = 1 + 1/4 add them up to get 2+1 + 3/4 + 1/4 = 3 4/4 = 4
*June 6, 2014*

**Write each expression using a single exponent.**

when dividing, just subtract exponents: 5^10 / 5^7 = 5^(10-7) = 5^3 because 5^10 = 5*5*5*5*5*5*5*5*5*5 5^7 = 5*5*5*5*5*5*5 divide, and seven of the 5's cancel, leaving only 3 in top: 5^3 76^11 / 76^5 = 76^(11-5) = 76^6
*June 6, 2014*

**wdwd**

csc(4θ+3) sin(5θ-6) = 1 That's surely an odd sort of expression. Still, since cscθ = 1/sinθ, we have sin(5θ-6) = sin(4θ+3) So, we want 5θ-6 = 4θ+3 θ = 9 That seems kind of big, so what if we consider that sin(π-x) = sin(x...
*June 6, 2014*

**maths**

72000(1+.80n) = 87840 1+.80n = 1.22 and so on to get n
*June 6, 2014*

**math**

v = x^3, so dv/dt = 3x^2 dx/dt = 6(2t+1)^2
*June 6, 2014*

**Math**

since multiplication is commutative, 3 * 10^6 * 2 * 10^12 = 3*2 * 10^6 * 10^12 = 6 * 10^18 the other is analogous. Just recall that 30*10^13 is not scientific notation.
*June 6, 2014*

**Math**

3x^2+2x-x^2+3 3x^2-x^2+2x+3 (3-1)x^2 + 2x + 3 2x^2 + 2x + 3 not much to do -- just combine the x^2 terms. We used commutativity of addition and distributive property.
*June 6, 2014*

**trig**

cosA/(1-tanA) + sinA/(1-cotA) cosA/(1-tanA) + sinAtanA/(tanA-1) (cosA - sinAtanA)/(1-tanA) (cos^2A-sin^2A) / cosA(1-tanA) (cos^2A-sin^2A)/(cosA-sinA) cosA+sinA sure you don't have a typo somewhere?
*June 6, 2014*

**trig**

since cosA = 5/13, sinA = 12/13 Now just use those values in your double-angle formulas.
*June 6, 2014*

**MATH**

wolframalpha.com is your friend. For #26, see http://www.wolframalpha.com/input/?i=table+2x^2-4+for+x+%3D+-3+..+5
*June 5, 2014*

**help needed with math**

Was something wrong with the solution I posted here? http://www.jiskha.com/display.cgi?id=1401907573
*June 5, 2014*

**math**

4/52 * 4/51
*June 5, 2014*

**MATH**

#14. For each x, place a 3. f(3) = 4*3-4*3-7 = -7 Same way for #16 However, I suspect a typo, since 4x-4x-7 = -7 for any value of x.
*June 5, 2014*

**algebra**

clearly, 4y = (2/3)x - 8 so, 24y = 4x-48 -4x + 4x-48 = 32 -48 = -32 No solution exists
*June 5, 2014*

**Can you help me find the answers?**

#10 14-11*1 = 14-11 = 3 14-11*2 = 14-22 = -8 ... #12 23+1 = 24 23+2 = 25 ...
*June 5, 2014*

**Find the common difference or ratio in each..?**

6: r = 1/4 8: r = -2 That should do it.
*June 5, 2014*

**Math**

48000(1+.0428/12)^18 = 51,176.82
*June 5, 2014*

**math Study guide**

1A 2B 3C 4C 5B Whenever there is replacement, then the events do not affect each other. Or, if the events are unrelated, as with dice and spinners, they are independent. 6: 1/2 * 1/2 = 1/4 7: 1/2 * 3/6 = 1/4 8: 20 total marbles, so 7/20 * 6/20 9: 1/2 * 3/6 (primes are 2,3,5) ...
*June 5, 2014*

**math question check**

4/10 * 2/10 = 2/25
*June 5, 2014*

**math**

just plug in a value for n and compute the value for C. For example, if 10 people attend, n=10, and C = 10*10+26 = 126 So, the pair for that would be 10,126 Now use your numbers and finish it up.
*June 5, 2014*

**algebra**

that's "whether" not "weather". visit wolframalpha.com and just type in a function. It will show you the graph and other information. Be sure to note how interprets you input. You may need to use some parentheses to ensure proper evaluation. The graph ...
*June 5, 2014*

**math question**

No, that's 0.15 * 20 Look. 15% means you expect 15 wins in 100 tries. 20 is only 1/5 of 100, so you expect 1/5 as many as 15, or 3. 0.15*20 = 3 That is, 15% of 20 is 3.
*June 5, 2014*

**math question**

well, what is .15 * 20 ?
*June 5, 2014*

**math - eh?**

Can't say, since you have only presented an approximation to a question. Read what you posted, then supply all the missing data, so we have something to work with.
*June 5, 2014*

**mathematıcal lıteracy**

can't say, since you don't say how big the sides are. Also, I assume you mean that 1 litre covers 5m^2 of area. In any case, figure the area to be painted, in m^2, and then multiply that by R26/5m^2
*June 5, 2014*

**Geometery - incomplete**

you need to describe the diagram. What is the relationship between the angles? Suppose I ask you what color the fruits are. Have an answer? Also, try using symbols. The usual format is If m<1 = 43°, what is m<2? There is even an angle symbol which you can use: ∠
*June 5, 2014*

**MATH**

looks pretty standard to me. To play around with functions and their graphs, you can visit wolframalpha.com and just type in your function. For example, http://www.wolframalpha.com/input/?i=x^2-9
*June 5, 2014*

**math**

The usual reference level is 10^-12 W/m^2 Here, you have 2.37*10^-5 W/cm^2 = 2.37*10^-1 W/m^2 The dB level is thus 10 log(2.37*10^11) = 10*11.37 = 113.7 dB
*June 5, 2014*

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