Question

A man invested an amount at 12% per annum simple interest and another amount at 10% per annum simple interest. He received an annual interest of Rs. 2600. But, if he had interchanged the amounts invested, he would have received Rs. 140 less. What amount did he invest at the different rates.

Answer 1

Let the amount @ 12% be x and amount @ 10% be y

According to the first condition, we have

12x/100 + 10y/100 = 1145

12x + 10y = 114500 (i)

According to the second condition, we have

10x/100 + 12y/100 = 1145 - 90

10x + 12y = 105500 (ii)

Adding (i) and (ii), we have

22x + 22y = 220000

x + y = 10000 (iii)

Subtracting (ii) from (i), we have

2x - 2y = 9000

x - y = 4500 (iv)

Adding (iii) and (iv), we have

2x = 14500

x = 7250

Putting x = 7250 in (iii), we have

y = 10000 - 7250 = 2750

So, the amounts he invested are Rs. 7250 @ 12% and Rs. 2750 @ 10%