Roni obtained an amount of Tk. 6400 as simple interest on a certain amount at 8 p.c.p.a. after 5 years. What is the amount invested by Roni?

Question: Roni obtained an amount of Tk. 6400 as simple interest on a certain amount at 8 p.c.p.a. after 5 years. What is the amount invested by Roni?

Solution:
Suppose, Principal = Tk. 100
Then interest for 5 years at 8%
= 5 × 8
= Tk. 40.

Now,
If interest is 40 taka then Principal = 100
∴ If interest is Tk. 6400 then Principal = (6400 × 100)/40 Tk.
= 16000 Tk.