The compound interest earned by Sunil on a certain amount at the end of two years at the rate of 10% p.a. was Rs.420. Find the total amount that Sunil got back at the end of two years in the form of principal plus interest earned.  Choose the correct option.
A) rs . 2530 B) rs . 2430 C) rs . 2420 D) rs . 2410 E) rs . 2440

Rationale: "let the sum be rs . p p { [ 1 + 10 / 100 ] 2 - 1 } = 420 p ( 10 / 100 ) ( 2 + 10 / 100 ) = 420 [ a 2 - b 2 = ( a - b ) ( a + b ) ] p = 420 / ( 0.1 ) ( 2.1 ) = 2000 . amount = 2000 + 420 = rs . 2420 answer : c"
Answer: C