Maths Problem, sorry to have to post it on AO

[Prankster]

Hi All, I have a maths exam tommorow and I am revising, this is a question that I should be able to work out the answer to:

Easypac Soup Company produce small cylindrical tins of radius 3cm, and similar large tins of radius 5cm. If a small tin contains 243ml of soup, how much does a large tin contain?

Now, I think I have done the correct working to complete this question correctly. When I key that answer in on the website (BBC Bitesize Revision) it tells me that it is wrong.

None of the other maths sites provide a question like this one so I have decided to post it on Antionline. I know that there are a lot of very intelligent people here and was really hoping that one of you could provide me with the correct answer and working out. I know that antionline is not exactly a "come here and we can answer any maths question you like" kind of site, but as I mentioned earlier, this is a very intelligent community so I thought this is where I would get the best response.

Thanks in Advance, any help is greatly appreciated:

Prankster

[bludgeon]

Um, I really stink at math, but can't you just divide the 243 by 3, and multiply the result by 5? Fer uh, 405ml. Eh, heh, we're dealing w/ volumns, I have no clue. . .sorry, man.

[Negative]

The volume of a cylinder is pR²H where p = pi, R = radius, and H = height.

The question suggests that the heights of both cans are equal, so we don't have to worry about that.
Concentrate on the surface.
The surface of the smaller cylinder: pi x 3²
The surface of the bigger cylinder: pi x 5²

pi x 3²    243
-------- = -----
pi x 5²     Y

where Y is what we need...

I hope I don't have to tell you how to derive Y from that

[nebulus200]

V = (PI)r^2h

243 ml = PI (3cm * 3cm) * h

If you use the cm and find volume you get cubic centimeters...not milliliters... 1 cm^3 = 0.001 L = 1 mL

So with that info: 243 ml = 243 cm^3 / (3.1415 * 9 cm^2) = 8.59 cm = h

So I am assuming that by similar they mean same height since everything else is different

so V = (3.1415 * (5^2) * 8.59 = 675 mL

Cheers,

/nebulus


PS It didn't really matter here, but always watch your units...favorite way to trip people up it seems. And always try to write down exactly what you know, and what you don't, and you will usually find that you can take what you know to figure out what you don't.

[Negative]

675 is what you get from my formula, too, so there's a big chance it's correct...Heh.

[nebulus200]

Yeah, you beat me to it barely, but I left the post in there because it broke down how to get from point A to point B

That was kinda fun, haven't really had much of a reason to think about that kind of stuff in a few years now...

/nebulus

[Prankster]

Thanks guys, 675 is the answer that I thought was correct answer, yet when you key 675 into the answer box, this is what you get:

10. You said 675. Hard luck. You need to calculate the ratio of the volumes.



I think this is pretty poor for a website coming from the BBC, as I have come to expct good service from them. Especially on an exam revision question.

Thanks for all your help, it's really appreciated, anyway I've finished the exam now, it went OK and this wasn't even on it! Thanks Again-

Prankster