Answer: It will amount to 11p after 20 years.
Explanation:
Formula :
Simple interest = Principal x rate x Time (i)
Amount = Principal + Interest
Amount = Principal + Principal x rate x Time
Amount = Principal (1+ rate x Time) (ii)
Given: Principal = p
After 1 year , amount = 1.5p
After 3 years , amount = 2.5p
From (ii)
Amount after 20 years = p(1+ 0.5 x 20) = p(1+10)=11p
It will amount to 11p after 20 years.