The simple interest at the rate of 6% p.a. received on a principal of Rs. X was RS.482.40 when invested for 3 years in scheme A. If scheme B offered compound interest compounded annually at 10% p.a., what was the interest received by investing Rs. (X-680) for 2 years in scheme B ?

Interest earned when a sum of Rs. $$X$$­ was invested for 3 years in scheme A at 6% S.I.

=> $$\frac{X \times 6 \times 3}{100} = 482.40$$

=> $$X = \frac{482.40 \times 100}{18} = 2,680$$

=> Amount invested in scheme B = $$2,680 - 680 = 2,000$$

Interest received when Rs. 2,000 was invested for 2 years in scheme B at 10% C.I.

= $$2,000 [(1 + \frac{10}{100})^2 - 1]$$

= $$2,000 [(\frac{11}{10})^2 - 1] = 2,000 [(\frac{121}{100}) - 1]$$

= $$2,000 \times \frac{21}{100}$$

= $$20 \times 21$$ = Rs. $$420$$