Delhi Police Constable Exam Model Paper 7

GIVEN:
A sum of money becomes double in 20 years when invested at simple interest.
CONCEPT:
Simple interest concept.
FORMULA USED:
SI = (PRT/100)
Where,
P = Principal, R = Rate, T = Time
CALCULATION:
Suppose Principal = Rs. P, Amount = 2P, Time = 20 and Rate = R% (Suppose)
⇒ SI = 2P – P = Rs. P
Now,
P = (P × 20 × R/100)
⇒ R = 100/20 = 5%
∴ The rate of interest = 5% per annum