At what rate (in percentage) per year will a sum of money 5 times itself in 16 years on simple interest?

Correct option is B

Given
Amount becomes 5 times the Principal.
Time = 16 years.
Formula Used
Simple Interest (SI) = Amount - Principal
Rate = $$\frac{SI \times 100}{Principal \times Time}$$​​
Solution
Let Principal be P.
Amount = 5P
SI = 5P - P = 4P
Rate = $$\frac{4P \times 100}{P \times 16}$$​​

Rate =  $$\frac{400}{16} = 25\%$$​​
Final Answer
So the correct answer is (b) 
Exam Hall Method: