If the compound interest on a certain sum of money for 7 years at 10% per annum be Rs. 993, what would be the simple interest?  Options.
A) rs . 880
B) rs . 890
C) rs . 895
D) rs . 2100
E) none

Rationale: "let p = principal a - amount we have a = p ( 1 + r / 100 ) 3 and ci = a - p atq 993 = p ( 1 + r / 100 ) 3 - p ? p = 3000 / - now si @ 10 % on 3000 / - for 7 yrs = ( 3000 x 10 x 7 ) / 100 = 2100 / - answer : d ."
Answer: D