I really do not like to have an understanding hanging when learning, as it could crop up somewhere else in the future.

In my class, this question was simply to find the surface area of a cylinder that is 1 metre in diameter, and 2 metres in height.

The instructor had stated "You must convert it in to centimetres", and I did and it had worked - and I did not understand.

My two calculations that confuse me:

m:

$\displaystyle SA = 2\pi(.5)^2 + 2\pi(.5)(2) = 7.852 m^2 = 785cm^2$

cm:

$\displaystyle SA = 2\pi(50)^2 + 2\pi(50)(200) = 78539.82 cm^2$

It seems the two numbers are the same, even though wrong radix, however why can you not use metres? Does the calculation require it? That would not make sense, as (at least I believe) people would obviously use inches as a diameter in the states and other things.

It may just be something so simple, it is really bothering me.

Alexei.