Some principal becomes Tk. 1,560 as profit-principal in 3 years and Tk. 1,920 as profit-principal in 6 years. Find the rate of profit.

Question: Some principal becomes Tk. 1,560 as profit-principal in 3 years and Tk. 1,920 as profit-principal in 6 years. Find the rate of profit.

Solution:
Given,
Principal + Profit for 3 years = 1560
Principal + Profit for 6 years = 1920

So the profit of 3 years I = Tk. (1920 - 1560)
= Tk. 360

So the principal P = Tk. (1560 - 360)
= Tk. 1200

∴ The rate of profit r = (I × 100)/(P × n)
= (360 × 100)/(1200 × 3)
= 10