Hasan lent Tk. 400 to Asif for 2 years and Tk. 100 to Ratul for 4 years and received together from both Tk. 60 as interest. What is the rate of interest if the simple interest rate of both is the same?

Question: Hasan lent Tk. 400 to Asif for 2 years and Tk. 100 to Ratul for 4 years and received together from both Tk. 60 as interest. What is the rate of interest if the simple interest rate of both is the same?

Solution:
Let
rate is r%
The interest of Asif, I₁ = 400 × 2 × r%
The interest of Ratul, I₂ = 100 × 4 × r%

According to the question,
{(400 × 2 × r)/100} + {(100 × 4 × r)/100} = 60
Or, 8r + 4r = 60
Or, 12r = 60
Or, r = 60/12
∴ r = 5%