There is 50% increase in an amount in 5 years at simple interest. What will be the compound interest of Rs. 12,000 after 3 years at the same rate ?

Let p = Rs. 100.

Then, S.I is Rs. 50 and time = 5 years. 

$\therefore R = \frac{100\times 50}{100\times 5}$= 10% p.a.

Now, p = Rs. 12,000 , T = 3 years and R = 10% p.a.

C.I. = Rs. $12000\times 1+\frac{10}{100}3-1$= Rs. 3972