the difference between compound interest and simple interest on a sum for 2 years at 8 % p.a. is Rs. 768. Find the sum

Let the amount of money invested =M, then we have:

{M x [1.08]^2 - M} - {M x 0.08 x 2} = 768, solve for M

{ 1.1664M - M} - {0.16M} =768

0.0064M =768  Divide both sides by 0.0064

M = 768 / 0.0064

M =120,000 Rs - The principal amount invested. 

Compound interest =19,968

Simple interest =19,200

19,968 - 19,200 =768 Rs.