Two cylinders P and Q are mathematically similar.

The total surface area of cylinder P is 90pi cm^2

The total surface area of Cylinder Q is 810pi cm^2

The length of cylinder P is 4cm

Work out the length of cylinder Q

Method NOT answer please

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- Jan 7th 2010, 09:27 AMMukilabMathematically similar...work out length
Two cylinders P and Q are mathematically similar.

The total surface area of cylinder P is 90pi cm^2

The total surface area of Cylinder Q is 810pi cm^2

The length of cylinder P is 4cm

Work out the length of cylinder Q

Method NOT answer please - Jan 7th 2010, 12:26 PMMukilab
I'm guessing that it is 36.

The surface area of Q divided by the surface area of P is 4. So I take P's length and times it by 4 giving me 36.

I repeat this when it tells me to work out the volume. 100pi goes to 400pi. Or is it 100x4x4? - Jan 8th 2010, 01:06 AMaidan
$\displaystyle \dfrac{810}{90} = 9 $

The area has increased 9 times.

for a square:

if you double the sides you get 4 times the area.

if you triple the sides you get 9 times the area (see above)

if you quadruple the sides you get 15 times the area.

Quote:

Two cylinders P and Q are mathematically similar.

If the length of cylinder P is 4 then the length of cylinder Q would be 4*3.

You can compute the radius for cylinder P from the infomation given.

Then multiply by 3 to get dimensions for cylinder Q.

Does that make sense?

. - Jan 8th 2010, 02:46 AMHallsofIvy
Careful here! I and, I think, most people, would interpret "increased by 3" as meaning "+ 3". It would be better to say "multiplied by 3".

[qote]If the length of cylinder P is 4 then the length of cylinder Q would be 4*3.

You can compute the radius for cylinder P from the infomation given.

Then multiply by 3 to get dimensions for cylinder Q.

Does that make sense?

.[/QUOTE] - Jan 8th 2010, 02:56 AMProve It
"Magnified by a factor of 3" would be acceptable language in this situation.

- Jan 8th 2010, 08:58 AMMukilab
Thank you for the answers although I did understand by 3...