Sunday

September 21, 2014

September 21, 2014

Total # Posts: 25,114

**math**

The new machine completes 2/13 of the job. So, the older machine requires (11/13)/(1/15) = 12.7 hours to do the rest.
*September 11, 2014*

**math**

Hmmm. I may have been hasty. Anyway, if there are x oz. of $3.50 alloy, the rest (30-x) is the $7.00 alloy. So, check to be sure that the value of silver adds up: 3.50x + 7.00(30-x) = 6.30(30) x = 6
*September 11, 2014*

**math**

we've done a lot of these mixture problems for you. Why not try some yourself, and we can check your work...
*September 11, 2014*

**Math**

Do you not see that you are missing some data here?
*September 11, 2014*

**math**

Tell you what. I'll solve one, and you can try the others. Post your work if you get stuck. x^2-3(2x+3)=0 x^2-6x-9 = 0 x = (6±√(36+36))/2 = (6±6√2)/2 = 3±3√2
*September 11, 2014*

**Grade 10 Maths**

recall that the vertex of a parabola is at x = -b/2a In this problem, that is x = -20/-1 = 20
*September 11, 2014*

**1**

First, find the speed of sound, and then recall that distance = time * speed. Then, since time = distance/speed, divide that distance by the speed of light.
*September 11, 2014*

**Year 10 Alegbra**

A = 8w - 2w^2 As you recall, the vertex of a parabola (in this case, the maximum area) is achieved at x = -b/2a In this case, that's x = -8/-4 = 2 Or, you can note that the roots of A=0 are 0 and 4. The vertex is midway between the roots, at x=2.
*September 11, 2014*

**Year 10 Alegbra**

depends on what the question is, no?
*September 11, 2014*

**math**

so, you gonna share those roots with us?
*September 11, 2014*

**Math: pre calculus**

If the width of the pens is x, and the overall length is y, then 3x+y = 240 The area is a = xy = x(240-3x) = 240x - 3x^2 This is just a parabola, with vertex at x = 40 So, the pens are each 40 by 60 ft. As usual, maximum area is achieved when the available fence is divided ...
*September 11, 2014*

**mathematics**

just as x^a * x^b = x^(a+b) log(a*b) = log(a) + log(b)
*September 11, 2014*

**MATH**

ummm, 53x5 = 265
*September 11, 2014*

**Force of Gravity**

since F = GMm/r^2 when r doubles you have GMm/(2r)^2 = Gmm/4r^2 = GMm/r^2 * 1/4 = F/4
*September 11, 2014*

**Geometry**

we have if p then q we are told p is true, so therefore, q: the measure is 90 degrees.
*September 11, 2014*

**8th Grade math**

False who says they have to be spaced 1 degree apart? If they are spaced 1 minute apart, there are 60*360 = 21,600 rays
*September 11, 2014*

**Quantitative Reasoning (math)**

360/60 = 6
*September 11, 2014*

**8th grade math**

Nope.
*September 11, 2014*

**8th grade math**

False. Between any two points there is another. Following that reasoning, between any two points there are infinitely many others.
*September 11, 2014*

**Math**

The 10x10 cake is 5x5 pieces, so it takes 4+4=8 cuts to do the job. That is 5 seconds per cut. The 12x12 cake is 6x6 pieces, so it will take 5+5=10 cuts, or 50 seconds. Assuming a 12" cut can be made in the same time as a 10" cut!
*September 10, 2014*

**Math**

If the original selling price was s, then she paid 3*s(1-.20)+10
*September 10, 2014*

**Math**

If there were originally b boys out of s students in the class, b/s = 2/3 b/(s+2) = 3/5 Or, b = 2s/3 5b = 3s+6 So, 5(2s/3) = 3s+6 10s = 9s+18 s = 18 Now you should be able to answer the question.
*September 10, 2014*

**pre calculus**

You know that a parabola with vertex at (h,k) is y = a(x-h)+k So, we now have y = a(x+3) - 10 Now just plug in (2,-5) to find a.
*September 10, 2014*

**Geometry**

Now you know that RSP = PST = -17 So, since RST = RSP + PST, RST = -34 Not sure what the negative values indicate. Sure there's not a typo in the problem?
*September 10, 2014*

**Geometry**

Use your distance formula: AB = √((2-0)^2+(7-3)^2) = √(4+16) = √20 = 2√5
*September 10, 2014*

**math**

Actually, the volume of a cone is v = 1/3 π r^2 h
*September 10, 2014*

**math**

2(w + 2w-3) = 144
*September 10, 2014*

**Math**

1,2,3,4,5,6,7,8,9,10,11,12,13 add up to 91. So, it looks like we have 1,2,3,4,5,6,7,8,9,10,11,12,14
*September 10, 2014*

**math**

Not quite sure what you're doing there. If a side of the square is 45, its perimeter is 180. Thus, the perimeter of the triangle is 90. So, each side of the triangle must be 30.
*September 10, 2014*

**algebra 1**

If x >= 0, |x| = x If x < 0, |x| = -x So, from what we have above, x >= 0 x-2 < 0, or x < 2 So, 0 <= x < 2
*September 10, 2014*

**Trig**

If the nearer observer is at distance x from the obelisk, then we have h/x = tan 65° h/(x+25) = tan 44° so, eliminating x, just solve for h in h/tan65° = h/tan44° - 25 h = 25/(cot44°-cot65°)
*September 10, 2014*

**math**

400m / 92s = 4.35 m/s or, 400m / 1.533 min = 260.9 m/min
*September 10, 2014*

**college algebra**

If x oz. of 1% are used, then the rest (3-x) are 5%, so .01x + .05(3-x) = .04(3) x = 3/4 So, 3/4 oz of 1% and 9/4 oz of 5% Note that 4% is 3/4 of the way from 1% to 5%, so 3/4 of the total is the 5% strength.
*September 10, 2014*

**college algebra**

If x is at 8%, the remainder (22000-x) is at 6% so, .08x + .06(22000-x) = 1680 ...
*September 10, 2014*

**math**

just plug in your numbers: h(t) = -16t^2 + 84t + 60 assuming he kicks it straight up. Now just plug in t=2
*September 10, 2014*

**Math**

Since A+B+C=180, C=94.24 So, using the law of sines, c/sinC = a/sinA Now just plug and chug.
*September 10, 2014*

**Algebra!!!! HELP**

Since F=kx, F/x is constant. So, (a) 120/x = 265/0.15 (b) F/0.3 = 265/0.15 Note that you can answer these questions without even determining the value of k explicitly.
*September 10, 2014*

**math**

Just use the quadratic formula: x = (-(c-a)±√((c-a)^2 - 4(b-c)(a-b)))/(2(b-c)) You can play around with that some, but I don't see much in the way of simplification. http://www.wolframalpha.com/input/?i=%28b-c%29x%C2%B2+%2B+%28c-a%29x+%2B+%28a-b%29
*September 10, 2014*

**math**

(6x+2)/4 + (2x²-1)/(2x²+2) = (10x-1)/4x Clear fractions by using the common denominator of 4x(x²+1). This requires that x≠0. (6x+2)(x(x²+1)) + (2x²-1)(2x) = (10x-1)(x²+1) (6x^4+2x^3+6x^2+2x) + (4x^3-2x) = (10x^3-x^2+10x-1) 6x^4 - 4x^3 + 7x^2...
*September 10, 2014*

**calc**

If you found T(t) = r'/|r'|, then you should be able to get N(t) = T'/|T'| Where do you get stuck?
*September 10, 2014*

**math**

(1) 2(x + x-3) = x(x-3) x = 1 or 6 But x=1 isn't viable, so only x=6 (2) 2(x+x) = x^2 x = 4
*September 10, 2014*

**maths-calculus**

If you let u = -(x+1), you have u(e^(-1/u) - 1) = (e^(-1/u) - 1) / (1/u) Now using l'Hospital's Rule, that is the same as (e^(-1/u) - 1)(1/u^2) / (1/u^2) = e^(-1/u) - 1 -> 0-1 = -1
*September 10, 2014*

**Math**

I'd say -40 + 20 = -20
*September 10, 2014*

**math**

sounds like a good deal. Was there a question in there somewhere?
*September 10, 2014*

**math**

Since the density is obviously 2 seedlings/hill, I suspect you want the density in terms of seedlings/m^2 or something. Since each hill occupies 400cm^2, the density is 2 seedlings/400cm^2 = 1/200 seedlings/cm^2 Maybe not too useful. In terms of m^2, that will come out 2 ...
*September 10, 2014*

**programming**

Can you see what a useless question that is to be asking here? Any exposition you find here will only be what you can find in your text (if any) or in any of the sites turned up by google.
*September 10, 2014*

**math**

If Stevie sings x songs, then Christine sings x-6 songs. Add them up: 8 + x-6 + x = 18 x = 8
*September 10, 2014*

**Math!!**

yes. good job.
*September 9, 2014*

**Math**

You have an arithmetic progression where a = 20 d = 4 T20 = 20+19*4 = 96 S30 = 30/2(2*20+29*4) = 2340
*September 9, 2014*

**math**

8+(7) = 8+7 = 15
*September 9, 2014*

**mathematics**

In order to guarantee any reds at all, you need to draw 41, since the first 40 might be all green and white. So, 45 draws will guarantee 5 reds.
*September 9, 2014*

**Pre-Calculus**

easy. Just -5 to x and -4 to y: (-2,1) -> (-7,-3) and similarly for the other points.
*September 9, 2014*

**Algebra - typo?**

You know, we work hard to provide help with the problems. Don't make us read your mind as well. And shoot, why not show some of your own work to help us figure out what is troubling you? If you mean to find the solution to the system of equations -7x+8y=-8 -2x+6y=-6 If you...
*September 9, 2014*

**math**

they are approaching at the rate of 18 mi/hr They only had to cover 5 miles, so that took 5/18 hours In that time, Jim ran 10 * 5/18 = 25/9 miles
*September 9, 2014*

**Pre-Calculus/Trigonometry**

A is true because the 2nd entry for x is 5, and the 2nd entry for f(x) = 6 Now for the others, the domain is the set of x values. The range is the set of f(x) values. D is just like A. That should help some.
*September 9, 2014*

**Pre-Calculus/Trigonometry**

there's nothing to solve. Just evaluate the expression. I tend to think that you meant 3/(x+2) - √(x+3) but it's hard to say due to your carelessness with parentheses. If I got it right, then it just evaluates to 3/(7+2)-√(7-3) = 3/9 - √4 = 1/3 + 2 = ...
*September 9, 2014*

**Pre-Calculus/Trigonometry**

well, I'd say that it's 3/7+2-√7-3 Insert parentheses as need for proper evaluation!
*September 9, 2014*

**Physics**

the velocity changed by -44 m/s in 4.8s, so the acceleration is -44/4.8 m/s^2
*September 9, 2014*

**Math**

the minimum cost is found at the vertex of the parabola. As you recall, that is at x = -b/2a, or in this case x = 10/.5 = 20
*September 9, 2014*

**maths**

cos(t) = 1.5/3 = 1/2 t = π/3 or 60° Better review you standard 30-60-90 and 45-45-90 triangles. They pop up often.
*September 9, 2014*

**math- help needed badly**

The ship travels 20 miles in the time given. If we label the points S for ship (current position), N and F for Near and Far lighthouses, then if we call the original position O, In triangle SNF, S=25° N=125° F=30° In triangle ONS, n = 20 N=55° O=95° so, NS/...
*September 9, 2014*

**Calculus**

You have x,y r^2 = x^2+y^2, so r = √29 Now just plug and chug: sin = y/r cos = x/r tan = y/x and so on
*September 8, 2014*

**Precalculus**

75/x = tan 40° I assume you meant 40°, not 40', as that would have (a) been hard to measure (b) put the ship well over the horizon
*September 8, 2014*

**math**

Nope. C time to review
*September 8, 2014*

**AP CAlc. AB Please helppp!!**

As usual draw the graph. Clearly for r < 0, f(x) = -x + 1, so A(r) = ∫[-2,r] -x+1 dx For r > 0, we have f(x) as -x + 1 for -2 <= x <= 0 x + 1 for 0 < x <= r So, A(x) = ∫[-2,0] -x+1 dx + ∫[0,r] x+1 dx Both of those are easy to evaluate, so ...
*September 8, 2014*

**algebra**

width: w length: 2w+5 so, 2(w + 2w+5) = 46 Now you can get w, and then 2w+5.
*September 8, 2014*

**Pre-Calculus/Trigonometry**

Uh, look at the table. 1 is the 5th entry in the x row 1.3 is the 5th entry in the f(x) row. So, f(1) = 1.3
*September 8, 2014*

**Math Proof**

sure could. But the argument is the same. Might as well work with what you were given, in this case at least.
*September 8, 2014*

**Math Proof**

Looks good. This is the method usually used to prove that √2 is irrational, but it works for any integer. You can find lots of proofs for that online. Look some up, and see how they use the same argument.
*September 8, 2014*

**Math**

clearly, the deduction will be .062*3260 + .0145*3260 It will be the same for all her paychecks, since her annual earnings will fall well short of the SS cutoff point.
*September 8, 2014*

**MATH HELP**

Now: 46 At the end of Day 1: 38 Day 2: 30 Day 3: 22 Day 4: 14 - order more Day 5: 6 Day 6: out of stock unless more has arrived
*September 8, 2014*

**Math Proof**

sum: Assume that it is rational. That is, if c = a/b, then a/b + x = m/n for some integers m and n. That means that x = m/n - a/b But m/n-a/b = (bm-an)/(bn), clearly a rational number, and x is irrational. So, if x is irrational, c+x cannot be rational. Clearly, cx must also ...
*September 8, 2014*

**math**

Assuming you mean (6x)^2 = (6x)(6x) = 36x^2 or, (6x)^2 = 6^2 * x^2 = 36x^2
*September 8, 2014*

**math**

D additive identity = 0 multiplicative identity = 1 a+0 = a a*1 = a for any value of a
*September 8, 2014*

**math**

hint. substitute to get 6x + 4(3-3x) = 0
*September 8, 2014*

**math**

since there are three values of x which satisfy the equation, there are three values for 2x+3.
*September 8, 2014*

**math**

(3,4/3)
*September 8, 2014*

**math 1 question**

powers first: 25-4/5+2 then multiplication and division, left to right: 25 - 0.8 + 2 then addition and subtraction, left to right: 24.2+2 26.2
*September 8, 2014*

**Math**

You have 26*1760+385 = 46145 yards since 1 meter = 1.0936 yards, that means you have 46145/1.0936 = 42195 meters When you get stuck, it's best to post your work -- that way we can help figure out where you went wrong. Just sayin'
*September 8, 2014*

**algerbra**

divide the second by 3 and you will see that they are the same line.
*September 8, 2014*

**phycis**

since mass * distance is the same, and the heaver mass only rises 1/6 as far, it is 6 times the mass, or 360N
*September 8, 2014*

**Math**

what is 1000000/100? It's 10,000 So, 10,000 CDs to each of 100 stores makes 1,000,000. 925,733 The 2nd 3 is just 3 The others are true
*September 8, 2014*

**math**

Hmmm. If the sides are in the ratio 4:5:6, then the sines of the angles are in the same ratio (law of sines) So, if sinA = 4x, sinB = 5x sinC = 6x arcsin(4x)+arcsin(5x)+arcsin(6x) = pi x = √7/16 A = arcsin(4√7/16) = 41.41 B = arcsin(5√7/16) = 55.77 C = arcsin...
*September 8, 2014*

**Math**

Id say f(x) = x h(x) = 4 f(x)
*September 8, 2014*

**math**

since the slope is the same, they are either parallel or the same line. I expect you can decide which. If parallel, no solutions, since they do not intersect. If the same line, there are infinitely many solutions, since any point on one line is also on the other.
*September 8, 2014*

**algerbra**

well, did you try any to see whether they are? (0,-1): -1 = 6*0-1? yes and so with the others.
*September 8, 2014*

**calculus**

∂u/∂x = 2x/(x^2-y^2) ∂u/∂y = -2y/(x^2-y^2) ∂2u/∂x∂y = ∂2u/∂y∂x = -2(x^2+y^2)/(x^2-y^2)^2
*September 8, 2014*

**math check answers**

I like all your answers. On #2, the markup based on cost is indeed 67%. The markup based on salling price is 40%, since the $100 markup is 40% of the $250 selling price. Could be they had a typo in the question or mixed up the answers.
*September 8, 2014*

**Math**

24(1.06)^(2013-1626) = $1.49*10^11 you may adjust it depending on whether the final year was an entire year.
*September 8, 2014*

**math - eh?**

sounds like a good deal. Is there a question in there somewhere?
*September 8, 2014*

**Algebra**

width: w length: w+11 so, 2(w + w+11) = 90 Now just solve for w, and figure the length.
*September 7, 2014*

**Algebra**

How approximate? Assuming you meant f(x) = -8x^2 + 2x + 2, f(-1) = -10 f(0) = 2 f(1) = -6 So, f(x)=0 somewhere in (-1,0) and (0,1). You can, of course, use the quadratic formula to get an exact answer and then approximate with as many decimal places as you wish. See http://www...
*September 7, 2014*

**math - eh?**

Heck, I can't even figure out what the string of digits and slashes even means! Maybe some parentheses around the terms will help. And two = signs? What's up with that?
*September 7, 2014*

**math**

If there are x lbs of 4.40 tea, then the rest (120-x) is 2.30 So, we need 4.40x + 2.30(120-x) = 3.00(120) Now just solve for x.
*September 7, 2014*

**Math**

If P(x) = x^2-4x, then since P(x) = x(x-4), it has two x-intercepts. Q(x) = x(x^2-4) = x(x-2)(x+2) so Q has 3 roots. x^2-ax = x(x^2-a) = x(x-√a)(x+√a) so there are 3 roots With 3 roots, there must be 2 extrema. x^2+ax = x(x^2+a) since a>0, x^2+a can never be ...
*September 7, 2014*

**Calculus**

x + y − 1 = ln(x^5 + y^5) 1 + y' = 1/(x^5+y^5) (5x^4 + 5y^4 y') y'(1 - 5y^4/(x^5+y^5) = 5x^4/(x^5+y^5) - 1 y' = ((x-5)x^4 - y^5)/(x^5 + (y-5)y^4) At (1,0), y' = (-4)/(-1) = 4 So, the line is y = 4(x-1)
*September 7, 2014*

**math**

18s^9 t^3 - 2s^9 t^2 can be factored into 2s^9 t^2 (9t-1) No idea how that can be evaluated to 9. I suspect there is something missing or garbled in the problem statement as shown.
*September 7, 2014*

**math**

341-115 = 226 341-120 = 221 So, any value between 221 and 226 will produce a number between 115 and 120. Or, using a compound inequality, we have 115 < 341-x < 120 -226 < -x < -221 226 > x > 221
*September 7, 2014*

**math**

You can figure out the mass of silver, then do all the conversions of mass to volume and back, or you can note that density(Al)/density(Ag) = 2.57 So, volume(Al)/volume(Ag) = 2.57 But, the volume of a sphere scales as the cube of the radius, so the radius scales as the cube ...
*September 7, 2014*

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