Question

A sum of 125 becomes 216 in 3 years at certain rate of interest compound annually

Answer 1

a = p { 1 +r/100} ^ n
216=125 (1 + r/100)^3
216/125 =(1+r/100)^3
6/5=1 + r/100
1/5 =r/100
r =20%

Answer 2

216= 125(1+r /100)^3
216/125=( 100+r/ 100)^3
(6/5)^3= (100+r/100)^3
6/5 =100+r/100
600= 500+5r
600-500= 5r
100= 5r
r= 100/5=20%