The sum invested in scheme B is thrice the sum invested in scheme A. The investment in scheme A is made for 4 years at 8% p.a. simple interest and in scheme B for 2 years at 13% p.a. simple interest. The total interest earned from both the schemes is Rs. 1320. How much amount was invested in scheme A?

Let the amount invested in scheme A be Rs. x and that in B be Rs. 3x.
Then,
$$\eqalign{ & = \frac{{x \times 4 \times 8}}{{100}} + \frac{{3x \times 2 \times 13}}{{100}} = 1320 \cr & or,\,\frac{{32x}}{{100}} + \frac{{78x}}{{100}} = 1320 \cr & or,\,\frac{{110x}}{{110}} = 1320 \cr & \therefore x = \frac{{1320 \times 100}}{{110}} \cr & = {\text{Rs}}{\text{. 1200}}. \cr} $$