A sum was put at simple interest at a certain rate for 10 years . Had it been put at 5% higher rate , it would have fetched Rs.300 more. What was the Sum? Choose the most appropriate option:  A) s . 1200  B) s . 1300  C) s . 600  D) s . 800  E) s . 1200

Rationale: "at 5 % more rate , the increase in s . i for 10 years = rs . 300 ( given ) so , at 5 % more rate , the increase in si for 1 year = 300 / 10 = rs . 30 / - i . e . rs . 30 is 5 % of the invested sum so , 1 % of the invested sum = 30 / 5 therefore , the invested sum = 30 × 100 / 5 = rs . 600 answer : c"
Answer: C