A borrowed ₹4800 from B at 9% per annum simple interest for 3 years. He then added some more money to the borrowed sum and lent it to C for the same period at 12% per annum simple interest. If A gains ₹720 in the whole transaction, how much money did he add from his side?
Total amount of interest given by A to B = $$\frac{4800 * 9 * 3}{100}$$ = Rs.1296
Let extra amount added by A = X
Total amount of interest received by A to C = $$\frac{(4800 + X) * 12 * 3}{100}$$ = (1728 + 0.36X)
Now,
(1728 + 0.36X) - 1296 = 720
0.36X = 288
X = 800
Hence, extra amount added = Rs.800