# Algebra (Volume, Ratios)

• March 1st 2013, 01:16 PM
Fratricide
Algebra (Volume, Ratios)
The figure (fig) shows a solid consisting of three parts, a cone, a cylinder and a hemisphere, all of the same base radius.

The first part of the question asks us to find the volume of each part, in terms of w, s, t and π (pi):

Volume of cone = (1/3)πt2w

Volume of cylinder = πt2s

Volume of hemisphere = (1/2)*(4/3)πt3

The next part of the question reads:

i: If the volume of each of the three parts is the same, find the ratio w : s : t.
ii: If also w + s + t = 11, find the total volume in terms of π.

Aaaaaaaand I have no idea, nor am I expected to have an idea -- I was never actually taught how to do this, it was some kind of maniacal challenge set by my teacher to see how I would go about finding an answer.

Any help would be much appreciated. Thanks for your time.
• March 1st 2013, 02:51 PM
Prove It
Re: Algebra (Volume, Ratios)
Well start by setting two of the volumes equal to each other.

\displaystyle \begin{align*} \frac{1}{3}\,\pi\, t^2 \, w &= \pi \, t^2 \, s \end{align*}

and find the relationship between w and s. You should be able to form the ratio between them from there.
• March 2nd 2013, 01:35 PM
Fratricide
Re: Algebra (Volume, Ratios)
So I did (1/3)πt2w = πt2s and came out with s = (1/3)w and thus w = s/(1/3). I tried solving (1/3)πt2w = (1/2)*(4/3)πt3 for t but failed miserably.

Have I done this right? Also, what significance does this have in finding the ratio?
• March 3rd 2013, 07:16 PM
Fratricide
Re: Algebra (Volume, Ratios)
Bump. Anyone?
• March 3rd 2013, 07:46 PM
ibdutt
Re: Algebra (Volume, Ratios)
• March 3rd 2013, 10:01 PM
Fratricide
Re: Algebra (Volume, Ratios)
Quote:

Originally Posted by ibdutt

So how did you go from having (1/3)w = s = (2/3)t to having the ratio (6:2:3)?

And also, where did "k" come from?
• March 4th 2013, 12:39 AM
ibdutt
Re: Algebra (Volume, Ratios)
• March 4th 2013, 12:32 PM
Fratricide
Re: Algebra (Volume, Ratios)
Thanks heaps. One final question to clarify my understanding: do we divide by 2 to make each fraction (1/X), (1/Y), etc? (i.e to turn (2/3) into (1/3) we must divide it by 2 and thus all the others by 2)
• March 4th 2013, 08:35 PM
ibdutt
Re: Algebra (Volume, Ratios)
Yes we divide the fractions by a suitable number so that we have 1 in the numerator of each fraction, in this case we divide by 2.
• March 4th 2013, 08:36 PM
Fratricide
Re: Algebra (Volume, Ratios)
Thanks heaps.