On a sum of money, the S.I. for 2 years is $600, while the C.I. is $615, the rate of interest being the same in both the cases. The rate of interest is? Pick one:
A) 4 %
B) 5 %
C) 6 %
D) 7 %
E) 8 %

Rationale: "difference in c . i . and s . i for 2 years = $ 615 - $ 600 = $ 15 s . i for one year = $ 300 s . i . on $ 300 for 1 year = $ 15 rate = ( 100 * 15 ) / ( 300 ) = 5 % the answer is b ."
Answer: B