Question

at what rate percent will a sum of rupees 640 be compuded to rupees 774.40 in 2 years?

Answer 1

774.40 = 640 ( 1+r/ 100) ^2
774.40/640 = (1+r/100 )^2
7744/6400 = (1+r/100) ^2
1936 / 1600 = ( 1+r/100)^2
(44/40)^2 = ( 1+r/100)^2
leaving power both sides we get
44/40 = 1+r/100
(44/40)-1 = r/100
4/40 = r/100
1/10 = r/100
r = 10%