On a sum of money, the simple interest for 2 years is Tk. 320, while the compound interest is Tk. 340, the rate of interest being the same in both the cases. The rate of interest is -

Simple interest for 2 years is Tk. 320
⇒ Simple interest for first year = 320/2 = 160
⇒ Similarly, simple interest for the second year is also 160
Compound Interest for first year = 160
Compound Interest for second year = 340-160 = 180
we can see that compound Interest for the second year is more than
simple interest for the second year by 180-160 = 20
i.e., Tk. 20 is the simple interest on Tk. 160 for 1 year
R = 100 × S.I./PT
= (100 × 20)/(160 × 1)
= 12.5%