:rsm was founded in 1996. from 1996 to 1997, the number of students in rsm doubled. from 1997 to 1998 the number of students doubled again. by what percent did the number of students increase from 1996 to 1998?

Alright so lets start with an arbitrary amount of students. Just to help us visualize the problem.

Say, 100 students for the first year when it was founded?

So far,
1996 - 100 students

From 96' to 97', it doubles. So:
1996 - 100 students
1997 - 200 students

From 97' to 98', it doubles AGAIN.
1996 - 100 students
1997 - 200 students
1998 - 400 students

So, what the percentage increase from 100, to 400?

Well, 100 x 4 gives us 400, so it's a 400 percent increase.