# Posts by steve

Total # Posts: 52,278

**Math**

3x = # dogs 2x = # cats 3x+2x = 30 ...

**Chemistry**

the valence of Na is always +1

**Science**

2kW = 2000 J/s = 2000 Nm/s Now just convert that to kg

**math**

the yard is 5750x2200 GCD(5750,2200) = 50 so, using 50x50 cm stones will use the fewest Now just figure how many that will be.

**Math**

looks like you just want the sum of all the numbers from 1 to 10. If you list the numbers, you get 1 2 3 4 ... 8 9 10 Now pair them up, starting from the ends. Each pair adds up to 11. There are 10 numbers, so 5 pairs, adding up to 11*5 = 55 Since it looks like you are going ...

**math**

there are 6 possible outcomes, and only one is a success, so P(5) = 1/6 Now you want two independent events, so just multiply their probabilities. Of the 36 possible outcomes, only 1 is a success...

**math**

see the related questions below

**math**

see related questions below

**Physics**

take a look at the formula which gives the pendulum's period. It involves g, right? Look what happens if you replace g by g/6

**Math-college**

if it has real coefficients, then its complex roots come in conjugate pairs, meaning f(x) = a(x-2i)(x+2i)(x-4i)(x+4i) = a(x^2+4)(x^2+16) Now just find a that makes f(-1) = 85

**Math**

a garden is 2x15 yards in size. what is its area, in ft^2?

**Math**

(44-4)/4 = 10 Hint: 4+2 = 6

**building a stair system**

what do you mean by "length"? The circumference is 360? inches. The size of the steps affects the "length" to the top, but the slant height is ?(180^2+77.5^2) ? 196 inches

**MaTh**

You can do this one by inspection, since you know that 5*20 = 4*25 = 100 Still, to solve this kind of problem in general, follow the steps. Write what they tell you, then work for a solution: vt = 100 (v+5)(t-1) = 100 (v+5)(100/v-1) = 100 (v+5)(100-v) = 100v v^2+5v-500 = 0 (v-...

**science**

which given calendar?

**Math**

so, how do you have a 12th row in a 3-by-3 array?

**Math**

they occur where the denominator is zero (and the numerator is not zero)

**Vectors**

the three vertices determine a plane. The 4th point must lie in that plane, but you can pick any of the three points to be the "origin" relative to the other two.

**Algebra**

we have b = kc/d^2 So, bd^2/c = k is constant That mean you want b such that 9b/20 = 45*2^2/40 ...

**Math**

b = j+9 6(b+8) = 7(j+8) now just solve for b and j.

**math**

x(1 - 7/13 - (2/3)(6/13)) = 6 now just find x.

**maths**

Pick two points, one near A and the other near B. You will find the order does not change.

**science**

the initial upward velocity is 80 sin 25° = 33.8 m/s So, the height y = 35 + 33.8t - 4.9t^2 (a) t = 7.8 So, use that to find the horizontal distance traveled at 80 cos25° = 72.5 m/s Finally, find the x- and y-components of the velocity at t=7.8 to get the answers to (b)

**Angular motion**

the circumference of the wheel is 0.6? so, since there are 2? radians per revolution, the angular speed is 36 / 0.6? * 2? = 120 rad/s

**Physics**

He clearly did not accelerate at 10 m/s^2 for the whole 10 seconds, or the distance covered would have been 1/2 at^2 = 500m and his top speed would have been 100m/s. So, if he accelerated smoothly from 0-12 m/s over t seconds, then a = 12/t m/s^2 So we have (1/2)(12/t)t^2 + 12...

**@oops**

I see I can neither factor nor count. Go with Reiny.

**Maths**

7056 = 2 * 3528 = 2^2 * 1714 = 2^3 * 857 Now factor 857. You know there are no more 2's in there, so start with 3, and so on. So, what do you get? Since there are only three 2's, the square root will not be an integer, but will have a radical left over.

**Math - eh?**

Is that (a^q)-r or a^(q-r) etc. And is that comma supposed to be a period? That is, are the three items all to be multiplied together?

**math**

recall that (u-v)(u+v) = u^2-v^2 Now let u = 2?b v = ?(3a) and it falls right out

**geometry**

see related questions below

**math**

42

**Math**

don't know. some probably can do polar coordinates, but the implicit definition makes it tricky. They wouldn't look as nice as the online ones, that's for sure.

**Math**

first step: use real math notation (x^2+y^2-1)^3 = x^2 y^3 As with any function, just start plugging in values for x (or y) and solving to get the other coordinate. Not easy, in this case, since high powers are difficult to solve except in special cases. The other, easier, way...

**math**

not even close. That 25 in there doesn't just disappear...

**math**

(30*25*14)/42 = ?

**calculus**

I guess that would just be ?[-5,5]?[0,?(25-x^2)] y dy dx = 250/3

**maths**

the job is 12*6 = 72 man-hours of work. In 1 hour, the 12 men have done 1/6 of the work, leaving 60 man-hours to do. That will take 20 men 3 hours to finish up.

**math**

if you mean 16% is 832, then .16x = 832 ...

**Math**

hmmm. You need to review just what "isosceles" means ...

**math**

any situation where one quantity changes steadily. All you need are two pairs of data relating the items

**math**

the 25% + 2/9 of the remaining 75% add up to 1/4 + (2/9)(3/4) = 9/36 + 6/36 = 15/36 = 5/12 So, if he started out with x limes, then 7/12 x = 280 and so on

**math**

since the only difference is an ice cream, it clearly cost $10 That means that the cake was $200 ...

**algebra**

If you set up the curves as described, you have x^2/25^2 + y^2/20^2 = 1 x^2/125 - y^2/100 = 1 They intersect at (±25?5/3,±40/3) so pick P to be one of those points and figure your answer.

**algebra**

you need to review your material. The mode is the value which occurs most often. So, what do you think?

**math/econ**

recall that the elasticity is (dx/dp)(p/x) = (40)(p/(40(p-15^2)) = p/(p-15^2)

**Maths**

cubics are not easily done in general, but a little synthetic division should quickly show you that you have (x-1)(x^2-6x+5) and that is easy...

**science**

all of them, I guess ...

**Math**

We can assume that Lisa has 3 and Betty has 5, so (3-1)/(5+1) = 2/6 = 1/3

**Arithmatic Progression**

why post it twice? Using your formulas, you see that 5/2 (2a+4d) = 40 a+6d = 4(a+d) Now you can find a and d, and thus the sum of the 2nd five terms is the sum of the first 10, less the sum of the first 5: 10/2 (2a+9d) - 40

**Statistics**

you can play around with Z table stuff here: http://davidmlane.com/hyperstat/z_table.html

**Maths**

clearly, the fastest has run one complete lap, while the slowest has run only 1/4 of a lap. Then if they started at the eastern side of the track, after 30 seconds they are at the points E,S,W,N in order of speed, fastest to slowest. After 30 more seconds, they are at E,W,E,W ...

**maths**

well, there were 1100-220=880 mangos, so ...

**Calculus 2 - Indeterminate forms**

it's quite simple. The rule states that lim f(x)/g(x) = lim f'(x)/g'(x) so, your limit is the same as (ln2*2^x-ln3*3^x)/-sinx(x) now, as x->0, that -> (ln2 - ln3)/0 = ? This is confirmed by the graph at http://www.wolframalpha.com/input/?i=(2%5Ex-3%5Ex)%2F(...

**Geometry**

the original block has surface 6*2^2 subtract the two circles removed: 2*?r^2 add the curved surface of the hole: 2?rh where r = 1/2 and h=2 the volume is of course 2^3 - ?r^2h

**pre calc**

draw a diagram. You can see that 5/x = sin ?/3

**Pre-Calculus**

Since profit is revenue less cost, we have p(x) = 150x - (0.02x^2 + 100x + 3000) now just find the vertex of that parabola.

**Calculus**

If the base has dimensions x and 2x, then we have 2x^2y = 10 so, y = 5/x^2 So, the cost of the container is c(x) = 12*2x^2 + 5*2xy + 5*xy = 24x^2 + 15xy = 24x^2 + 75/x so, find c(x) when dc/dx=0

**pharm**

15 mg/ml * 120ml = 1800 mg

**Physics**

You can easily adapt the example here to fit your problem: http://physics.bu.edu/~redner/211-sp06/class13/class13_rotation.html

**math**

9+x

**Math**

still the same: https://www.jiskha.com/display.cgi?id=1500466804

**algebra**

If your Revenue equation is corrected to read Revenue(x) = 5x then your Profit equation is correct. Not sure about the "need to make" clause. It's just what she makes.

**maths**

that's better

**maths**

That's not what I get. Where's your work? Did you try actually using your results to see whether they produce the desired AP?

**Math**

subtract the inner park from the total area: (350+2w)(200+2w)-350*200 = 74464

**Mathematics**

You got me. Aside from expanding into Taylor series and dividing, I don't come up with a trick to evaluate it.

**Math**

since all the sides are equal, the perimeter is just 3 times the length of one side.

**Physice - oops**

I should have said dynes, not ergs. Ergs are energy, not force.

**Physics**

Recall that F = ma so, just multiply. Note that the answer will be in ergs, not Joules.

**math**

homework is 2/3, so revision is 1/3 1/3 * 9/2 = ?

**math**

well, there are 360 degrees in the whole pie, so ...

**math**

well, 1/5 of 35 is 7, so ...

**arithmetic progression**

8/2 (2a+7d) = 56 20/2 (2a+19d) = 260 ...

**geometric progression**

probably best to first fins a and d: a+4d = 8 a+9d = -7 now subtract, and crank it out.

**Math**

If the mother is twice as old in x years, then we have 45+x = 2(12+x)

**Math**

(-6/7+18/28)*-7/5 = (-24/28+18/28) * -7/5 = -6/28 * -7/5 ...

**Mathematics**

b/g = 3/4 (b-3)/g = 5/8 b+g = 42

**Math**

well, we do know that (1+.035)^10 = 1.4106 (1+.035/4)^(4*10) = 1.4169 ... e^.035 = 1.4191

**geometry**

h/27 = sin 47°

**Math**

a*-1/27=1/18 a=-7/6 Bzzzt. a = -3/2

**maths**

80*3 = 60*4 = 240

**Physics**

draw a diagram of the velocities. Recognize an 8-15-17 right triangle?

**Math**

No one asked how many fruits there are. You just need to give the fraction. Read the question carefully.

**Math**

3/5 + 1/4 = 12/20 + 5/20 = 17/20 so, what do you think?

**Calculus - incomplete**

What does the coastline look like? Is it straight? N-S, E-W? All I know for sure just now is that the radar station lies somewhere on a circle of radius 1.5 with its center at the port. Anyway, draw a diagram. It should be clear how to use the available angles and distances to...

**math**

No way to tell. However, if the function has rational coefficients, then the irrational roots must occur in conjugate pairs. Thus, the other root must be 3-2?2

**college algebra**

Let x = amount in bonds Then 68000-x is the amount in CDs Now just add up the interest: .08x + .07(68000-x) + .10*68000 = 12040

**Science**

total energy = PE + KE = mgh + 1/2 mv^2 Now just plug in your numbers

**math**

8 is 16% of the 50 sampled. That means that 200 is 16% of the whole population. 0.16p = 200 ...

**Quadratic Equation - Henry**

max height reached at t=2 h=0 at t=5 so, 2 seconds rising, 3 seconds falling he got the 3 by seeing how long it takes to fall 144 ft. s = 1/2 at^2

**Math**

Certainly not English -- the units are metric! To get the width of the path, subtract the inner garden area from the total: 40*25 - (40-2w)(25-2w) = 126

**Calculus**

the derivative is -x/50 + 50 maximum revenue occurs when that is zero.

**Chemistry**

what don't you understand? Surely you can at least pick out the elements, and then see which are atoms and which are molecules. And take a stab at the compounds; the ionic ones usually involve a metal and a halogen.

**AOOOGAH!! Homework Dump!!**

no ideas on any of these? We're not here to do your homework for you...

**Physics**

a = 2 m/s^2 means that v grows by 2 m/s every second. So, what do you think? v = at

**algebra**

recall that the vertex of a parabola ax^2+bx+c is at x = -b/2a

**Algebra**

g(x) is written in the slope-intercept form. Its slope and y-intercept should be obvious. For f(x), note that y changes by 2 when x changes by 1 f(0) = -1 ...

**decreased by twice a number**

if the number is x, what is twice the number? 2x what is 6 decreased by 3? 6-3 so, what do you think?

**Algebra**

each element must be identical in the two matrices (you already have 1=1 and 3=3), so you just have to solve 5x-8 = 2 4m-1 = 7m+6 then use those values to fill in the unknown elements.

**Calculus**

you have a point and a slope, so just use the point-slope form, which you learned in Algebra I: y+4 = 5(x-2)