How to Quickly find Rate of Simple Interest

Question:- A sum of money at SI amounts to Rs. 550 in 5 years and Rs. 600 in 6 years. What is the Principal and the Rate of Interest?

Solution: We know that simple interest is same for all the years. So we find the difference in the number of years and the amounts.

The difference in number of years = 6 – 5 = 1 year
The difference in amounts = Rs. 600 – Rs. 550 = Rs. 50
∴ Simple Interest = Rs. 50/ 1 year = Rs. 50/ year
∴ SI for 6 years = 50 × 6 = 300

Principal Amount = Amount after 6 years – SI for 6 years