A certain sum of money is invested at an interest rate of 5% per annum and a second sum twice as large as the first is invested at 5.5% p. a. The total amount of interest earned from two investments together is Tk. 1000 per year and the interest is withdrawn every year. The first sum invested is:

Question: A certain sum of money is invested at an interest rate of 5% per annum and a second sum twice as large as the first is invested at 5.5% p. a. The total amount of interest earned from two investments together is Tk. 1000 per year and the interest is withdrawn every year. The first sum invested is:

Solution:
Let
Two sums Tk. x and Tk. 2x

Now
{(x × 5 × 1)/100} + {(2x × 5.5× 1)/100} = 1000
5x + 11x = 100000
16x = 100000
x = 6250

The first sum = Tk. 6250