# Posts by steve

Total # Posts: 52,263

**Chemistry**

well, 1 mole occupies 22.4L so, how many moles do you have?

**science**

PE = mgh so, m*9.8*1.5 = 44.1 now just crank it out...

**geometry**

48/x = tan 15°

**geometry**

First is always draw a diagram. Then review your basic trig functions. It should be clear that the distance between the boats is 150 cot 12.5° - 150 15.3° You will also see this problem where you want to find the height, given the distance between two points on the ...

**math**

A?B = {(1,3),(2,2),(3,1),(3,2)...(3,6),(2,3)...(6,3)} A?B = {(1,3),(3,1)}

**Math**

https://www.jiskha.com/display.cgi?id=1499370105

**math**

every multiple of a 3-4-5 triangle would lie on the grid.

**math**

clearly, x must be a multiple of 5*42 = 210 I get 101010 = 42*2405 = 210*481

**Math**

(?3-?2)^2 = 3-2?6+2 = 5-2?6 so that means you have 5-2?6 - 3?3 + 3?2) + 4 = 9 + 3?2 - 3?3 - 2?6

**Math**

If a+2b=60 that is just like the problem of finding the maximum area enclosed on three sides by 60 ft of fencing. That is when a=30 and 2b=30. So, maximum ab = 30*15 = 450 f(x) = x^2 - 3x + 4 f(?3-?2) = (?3-?2)^2 - 3(?3-?2) + 4 The mean is (90+x)/5 = 18 + 0.2x arranged in ...

**@oops**

4-3/8 = 29/8, not 31/8

**Math, algebra**

If I read this right, x<>y = ?(xy)/|x-y| so, 9<>1 = ?(9*1)/|9-1| = 3/8 4<>(3/8) = ?(4*3/8)/|4-3/8| = ?(3/2)/(31/8) = 4/31 ?6 f(-1) = 3*1-5 = -2 f(-2) = 3*4-5 = 7 so, f(f(-1)) = 7

**algebra - and ... ?**

Assuming you meant f(x) = 160 * 2^x

**Geometry**

well, it appears that m?A=m?Q, so x-10 = 2x-30 solve for x, then m?A=x-10

**Math**

?r^2 = 78.5, so r=?(78.5/?) C = 2?r = 2??(78.5/?) = ?(314?) ? 10??3

**Math**

well, you know that 9/10 are either blue or red. So, 1/10 are yellow. If you can ascertain how many yellow balloons there are, then you can figure out the total.

**general math**

Just divide: (2x^2-4x+5)/(3-x) = -2x-2 + 11/(3-x) As x gets huge, the 11/(3-x) becomes negligible, and the asymptote is thus y = -2x-2

**Maths**

I assume you can find the volume of a cylindrical coin. For the frustrum, consider it as a large cone with a small cone cut off the top. If you draw a side view, then if the height of the small top cone is h, you have (h+9)/5 = h/3 h = 27/2 Now you see that the volume of the ...

**Maths**

the three numbers are 2x,3x,5x since there is a common difference, (3x-5)-2x = 5x-(3x-5) solve for x, and you can then answer the question.

**math**

since 9 >= 2u+3, the units digit can only be 0,1,2,3. Since the number is even the only starting points are 3x0xx0 7x4xx2 Fill in the x's with whatever you want.

**Math**

The center lies on the perpendicular bisector of the chord joining (0,0) and (5/2,1/2). That chord has slope = 1/5 midpoint = (5/4,1/4) So, the bisector is the line y - 1/4 = -5(x - 5/4) The center of the circle is at the intersection of the bisector and the line 2y=3x. So, ...

**maths(percentage)**

(.90 * .85)x = 7650

**maths(percentage)**

.70*.60 + .75*.40 = .72

**maths(percentage)**

10800 * 1.15 * 1.15 = ?

**Help me again in stats**

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

**Discrete or continuous help**

well, can you count them?

**math**

so, have you actually done any of that?

**chemistry**

.025 moles/L * 0.5L = .0125 moles NaCl so, how many grams is that?

**STATISTICS**

15 total marbles, so P(yellow,orange) = 7/15 * 3/14

**CALC**

in that case, it is clear that there are no asymptotes of any kind. f(x) is undefined at all for x^2 > 4 the graph is here: http://www.wolframalpha.com/input/?i=x%E2%88%9A(4-x%5E2)

**Maths**

If the roots are a and 1/a, then a*1/a = k/2 k=2 2x^2-7x+2 has roots (7±?33)/4 and, it happens that (7-?33)/4 = 4/(7+?33)

**Calc**

y = x?(4-x^2) y' = ?(4-x^2) + x * -2x/2?(4-x^2) = ?(4-x^2) - x^2/?(4-x^2) your answer is correct. Or, you can go on to make it (4-2x^2)/?(4-x^2)

**physics**

1m = 1.0936 yd 1m^2 = 1.196 yd^2 so, the cost is $18.95/yd^2 * 1.196yd^2/m^2 = $22.66/m^2

**Geometry**

in a parallelogram, adjacent angles are supplementary. If they are also congruent, they must be right angles. So, C is correct. You know nothing about the side lengths.

**maths**

x + 2x+30 = 150

**Math - woefully incomplete**

A bit more context is needed, doncha think?

**maths**

clearly the 1st digit is 1, so 1xxx Next, we see that we need 1x3x I'm sure you can take it from there, right? There are lots of valid answers.

**Maths**

1/2 + 1/3 = 5/6 so, only 1/6 of the bridge is over water. x/6 = 50 ...

**Math**

y = x/2+10 z = (x-y)/2+10 1/5 (x-y-z) = 5 x = 160 check: he spent 160/2+10 = 90, leaving 70 he spent 70/2+10 = 45, leaving 25 he spent .80*25 = 20, leaving 5

**Physic**

how long does it take the egg to fall 46-1.8 = 44.2 m? 4.9t^2 = 44.2 t = 3.00 s During those 3 seconds, Abu has walked 3*1.2 = 3.6 m

**physics**

well, his final position in relation to his starting point is (-3cos50°-2cos20°,3sin50°-2sin20°) = (-3.808,1.614) and as usual, velocity = distance/time

**Math**

L+K = 300 2/5 (L-112) = 5/6 (K-40) 2/5 (L-112) = 5/6 (300-L-40) L = 212

**Math**

why the minus sign? Reflecting across y=x is just like finding the inverse function. In other words, you have x = y^3+2y^2 see the graphs at http://www.wolframalpha.com/input/?i=plot+y%3Dx%5E3+%2B+2x%5E2,+x%3Dy%5E3%2B2y%5E2,+y%3Dx

**Maths**

Now, two questions: Do you mean (a) Cos(4?)/cos(2?) + sin(4?)/ sin(2?)=1 Cos^4(?)/cos^2(?) + sin^4(?)/ sin^2(?)=1 ?? and (b) what do you want to prove ??

**Math**

(x^2+1)/(x^2-1) = 221/220

**math**

119^2 - 111^2 = 14161-12321 = ? or 119^2 - 111^2 = (119+111)(119-111) = 230*8 = ?

**Math**

none needed, since multiplication is done before addition.

**Math**

b+g = 340 2/5 b = 4/7 g 2/5 b = 4/7 (340-b) b = 200

**Math**

2999

**math**

5(2x-3y = 6) 3(-3x+5y = 0) 10x-15y = 30 -9x+15y = 0 now add: x = 30 ...

**Math**

c + 3c = 84 ...

**Math**

x + 5x = 120 ...

**Maths**

z = 1+cos2? + i sin2? we want z = r(cosØ+i sinØ), where cosØ = 1+cos2? sinØ = sin2? That means that (1+cos2?)^2 + sin^2(2?) = 1 2 + 2cos2? = 1 cos2? = -1/2 cosØ = 1 - 1/2 = 1/2 sinØ = ?3/2 Ø = ?/3

**algebra**

that's what parentheses are for! a/(a+a^2) = a/(a(1+a)) = 1/(1+a) if a?0

**Geometry**

This is easy, since it's a right triangle. In fact, if you plot the points, you can easily see that it is a 3-4-5 triangle. So, the perimeter is ...

**maths**

the quotient is (4/7)÷(3/5) = 4/7 * 5/3 = 20/21

**geometry**

x^2+4y^2+2x+24y+28=0 x^2+2x + 4y^2+24y + 28 = 0 x^2+2x+1 + 4(y^2+6y+9) + 28-1-4*9 = 0 (x+1)^2 + 4(y+3)^2 = 9 (x+1)^2/9 + (y+3)^2/(9/4) = 1 Now we see that a=3, b=3/2, so c = 3?3/2 the foci are at (-1±3?3/2,-3) see http://www.wolframalpha.com/input/?i=ellipse+x%5E2%2B4y%...

**maths**

w = 3s w+12 = 2(s+12)

**@DrBob222**

What, there isn't any kind of double-replacement reaction that can swap metals like that?

**chemistry**

DrBob222 may have the right of it. And besides, my reaction "equation" is backwards. We wanted to produce the Al2(SO4)3, not use it. But then, I'm sure you caught that, right?

**chemistry**

well, the bare-bones equation is of the form Al2(SO4)3 + x -> 3CuSO4 + x so, each mole of Al2(SO4)3 produces 3 moles of CuSO4. Just convert your grams to moles, and work it from there.

**Math**

the 1st digit must be 9, so start there and use the largest unused digit in each next place. Just make sure the last digit is odd.

**Math**

a whole jug is 8 times as much as 1/8 jug, right? so 8 times as much juice ... I notice that the # pints produced is irrelevant ...

**Maths**

6 degrees in 6 hours. what do you think? (and it looks more like a decrease than an increase, to me)

**Math**

well, clearly the 1st digit must be 1, so I'd say with repeats: 100 w/o repeats: 102

**intro to algebra**

since d = km, d/m=k is constant. So, you want d such that d/5 = 20/3

**math**

1+2+3+...+n = n(n+1)/2 so, from 1:00 to 12:00 it strikes 12*13/2 = 78 times and it does that twice in 24 hours.

**Science**

1/2 a * 10^2 = 500 a = 10 m/s^2 v = at = 10*10 = 100 m/s

**math**

the numerators and denominators are elements of the Fibonacci sequence: 1,1,2,3,5,8,13,21,... so the next fraction is 8/13 Each numerator and denominator is the sum of the previous two.

**math**

(a,b,c) = (3,5,-8) so abc = -120

**Pre-calculus**

the center is on the line y = 2/3 x (the radius is perpendicular to 3x+2y=0). So the equation is (x-h)^2+(y - 2/3 h)^2 = r^2 using the given points, we have (1-h)^2 + (-1 - 2/3 h)^2 = r^2 (6-h)^2 + (0 - 2/3 h)^2 = r^2 solve for h and r, and our circle is (x-3)^2 + (y-2)^2 = 13...

**fraction**

e = 5r e - e/4 + 1/6 (r + e/4) = 90 + 5/6 (r+e/4) 5r - 5r/4 + 1/6 (r + 5r/4) = 90 + 5/6 (r+5r/4) r=40 so, e=200 check: Esther has 200, Richard has 40 Esther gives Richard 50 cards. Now they have Esther: 150, Richard: 90 Richard gives Esther 15, so they now have Esther: 165, ...

**Math**

18 = 2*3^2 25 = 5^2 35 = 5*7 so, any number divisible by all of those must be a multiple of 2*3^2*5^2*7 = 3150 so, what is the largest such number less than 10000?

**Physics**

the initial downward speed is 25/2 ft/s so, how long does it take to hit the ground? h(t) = 50-12.5t-16t^2 = 0 now, using that t value, recall that v(t) = -12.5 - 32t the horizontal speed is constant, at 25*0.866 ft/s

**trignometry**

reduce them by 360 until the values are between 0 and 360. So, sin 480° = sin(480-360) = sin 120° Now, you have to consider which quadrant you are in. sin 120° = sin(180-120) = sin 60° = ?3/2 sin 270° = sin(-90°) = -sin(90°) = -1 Now review this ...

**Math**

or, if we eliminate the "consecutive" then we have If the difference of two numbers is 15 and the greater of them is X then the smaller number is X-15

**math**

2010

**science**

density = mass/volume v = 4pi/3 r^3 I assume you know the mass.

**pre-calculus**

the wheel has a radius of 30, so y = 30sint or 30cost people get on at the bottom, so at t=0 y is at its minimum y = -30cost the minimum is at y=2, so y = 32-30cost the period is 20. y=cos(kt) has a period of 2?/k, so 2?/k = 20. k=?/10 y = 32-30cos(?/10 t) see http://www....

**Math**

the function is undefined where the denominator is zero. That is, tan(3x) = 0 this occurs when 3x = n? or, x = n * ?/3 where x=n? the function is 0/0, so there are holes there. the function is also undefined when the numerator or denominator is undefined. That is, when 3x or x...

**math**

so far, so good. To get the meeting point, set the two expressions for y equal to each other: -x/7 + 3/7 = -2x/15 + 6/15 x = 3 Now use that in either original equation to find that y = 0 So, the lines intersect at (3,0) However, you were asked to use an augmented matrix. You ...

**accountancy**

value to be depreciated: 108000-12000 = 96000 12 years to depreciate means 8000/year see what you can do with that.

**Maths**

well, the surface area of the roller is 84?*120 cm^2 so, divide the total area by that amount.

**math**

clearly the lines meet, since they have different slopes. So, what is your matrix?

**math**

1st step: what is the half-life of the original element?

**math**

this is exponential growth. Since it doubles in 2 hours, the population is after t hours is p(t) = A*2^(t/2) So, it will be 5 times as big as at first when 2^(t/2) = 5 or, you can start from scratch, using dp/dt = kp dp/p = k dt lnp = kt+lnA p = A*e^(kt) and work it from there

**math**

that would be HCF(2,4) so, what do you think?

**Number Theory**

If you want exactly 10 divisors, then the number will have to be a product of two primes, one raised to the 1st power, and the other raised to the 4th power. For example, 567 = 3^4 * 7^1 Its factors are 1 3 7 9 21 27 63 81 189 567 see why at http://www.wikihow.com/Find-How-...

**math**

it would grow by a factor of (6/5)^.8

**math**

?c^2 = c if c>=0 ?c^2 = -c if c<0 the ? is always positive or 0 ?16 = 4 ?4^2 = 4 ?(-4)^2 = 4

**Maths**

not sure what you mean by solving "harmonically," but sin(32.579°) ? 7/13 so, x+67.4 = 32.579 or adjust for the appropriate quadrant.

**math**

56*(24/16)*4

**Math - Calc 2/Algebra**

so far, so good. You now have 10x^2+2x-2 = Ax(x+1)+(-2)(x+1)+(6)x^2 10x^2+2x-2 = Ax^2+Ax-2x-2+6x^2 10x^2+2x-2 = (A+6)x^2 - (A-2)x - 2 for those two polynomials to be identical, all the coefficients must match. That is A+6 = 10 A-2 = 2 So, A=4 Luckily, those two equations give ...

**Math - Calc 2**

let x = 2sin? 4-x^2 = 4-4sin^2? = 4cos^2? dx = 2cos? d? Then you have ? x^2/?(4-x^2) dx = ?4sin^2?/2cos? * 2cos? d? = ?4sin^2? d? = ?2(1-cos2?) d? ...

**Math**

don't be scared by the awkward numbers. If I say that the sum of two numbers is 12 and one of them is 8, how do you find the other? 8+x = 12 x = 12-8 so, just follow the same steps with your numbers.

**math**

assume a linear relation. Then you need a constant slope to the function: (x-25)/(50-12) = (175-x)/(100-50) or 25/12 - x/50 = x/50 - 175/100 depending on how you are defining the decrease

**Number theory**

I think it's your turn now, eh? Whatcha got?

**Number theory**

google casting out nines and so on.

**Number theory**

Ahh I see you meant base, not scale. 550 = 10001001102 550 = 6719 what do you get for the others?

**Number theory**

2+5+6+9 = 22 550/22 = 25, so multiply all the values by 25. 1645 done that way will give fractional values.