Bihar Police Constable Model Paper 2

Given:
Amount becomes double in 12 years
Formula Used:
Simple Interest = (P × r × t)/100
Amount = P + Simple Interest
Where P → Principal
r → Rate of interest
t → Time
Calculation:
Let principal be 100
Amount = P + Simple Interest
⇒ 2 × 100 = 100 + Simple Interest
⇒ Simple Interest = 100
Simple Interest = (P × r × t)/100
⇒ 100 = (100 × r × 12)/100
⇒ r = 100/12
⇒ r = 25/3
⇒r = $8\left(\frac{1}{3}\right)\%$
∴ The rate of interest is $8\left(\frac{1}{3}\right)\%$.