Correct Answer - Option 1 : 5%

**Given:**

Money gets doubled in 20 years.

**Formula used:**

Simple Interest = (Principal × Rate × Time)/100

**Calculation:**

Time = 20 year

Amount double = 2p

Interest = 2p - p = p

Rate = (S.I. × 100)/(Time × Principal)

Rate = (p × 100)/(20 × p)

Rate = 5%

**∴ The rate of interest is 5%**