Saturday
September 20, 2014

Posts by Steve


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

maths
42
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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