# 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 ...

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)