For how much money will the profit at the rate of Tk. 5 per annum in 2 years 6 months be same as that of Tk. 1000 at the rate of Tk. 6 per annum in 4 years?

Question: For how much money will the profit at the rate of Tk. 5 per annum in 2 years 6 months be same as that of Tk. 1000 at the rate of Tk. 6 per annum in 4 years?

Solution:
Here are 2 parts,

In one part,
Given,
Principal P = Tk. 1000
Rate r = 6 per annum
Time n = 4 years

So simple interest I = (P × r × n)
= (1000 × 6/100 × 4)
= 240

In the other part,
I = Tk. 240
r = 5% = 1/20
n = 2 years 6 months
= 2.5 years

∴ P = I/rn
= 240/(1/20 × 2.5)
= (240 × 20)/(1 × 2.5)
= (4800 × 10)/25
= Tk. 1920