A sum of money was invested for “X” years in scheme A offering simple interest. The amount received after “X” years was twice the sum of money invested in the scheme. What will be the amount received from scheme A, when a sum of Rs 2800, is invested for “2X” years.

If amount after X years is twice the principal, then interest equals principal. In simple interest, if I = P in X years, then the rate r = 100/X %. For 2X years, the interest will be 2P (double the time). When Rs 2800 is invested for 2X years, interest = 2 × 2800 = Rs 5600. Amount = Principal + Interest = 2800 + 5600 = Rs 8400. This is option C.