A sum amounts to Rs.3969 in 2 years at the rate of 5% p.a. If interest was compounded yearly then what was the principal?  Choose the correct choice from the following answers:
A) s . 3600	B) s . 5000	C) s . 4500	D) s . 4800	E) s . 5800

Rationale: "ci = 3969 , r = 5 , n = 2 ci = p [ 1 + r / 100 ] ^ 2 = p [ 1 + 5 / 100 ] ^ 2 3969 = p [ 21 / 20 ] ^ 2 3969 [ 20 / 21 ] ^ 2 3600 answer : a"
Answer: A