If the annual income from a 5% stock at 90 is Tk. 40 more than the income from a 6% stock at 120, then what is the total investment?

Question: If the annual income from a 5% stock at 90 is Tk. 40 more than the income from a 6% stock at 120, then what is the total investment?

Solution:
Let,
The investment = Tk. x

5% stock at 90,
income from Tk. 90 = Tk. 5
∴ income from Tk. x = Tk. 5x/90
= Tk. x/18

6% stock at 120,
income from Tk. 120 = Tk. 6
∴ income from Tk. x = Tk. 6x/120
= Tk. x/20

ATQ,
x/18 - x/20 = 40
⇒ (10x - 9x)/180 = 40
⇒ x = 40 × 180
∴ x = 7200