Cpt question

The amount will be 9 times its principle in two years the rate if interest is

200
250
150
None of these

If,

A=PXNXR/100

900=100X2XR/100

R=900X100/100X2

  =450

But this answer is not there.

But,

If,

A=P(1+R/100)^N

900=1OO(1+R/100)²

^{30=10(100+R/100)}

^30=100+R/10

^300=100+R

^therefore,

^R=2OO

HOW WE WILL COME TO KNOW WHEN TO USE WHICH FORMULA?