# ML Aggarwal Solutions Class 9 Mathematics Solutions for Compound Interest Exercise 2.2 in Chapter 2 - Compound Interest

Question 22 Compound Interest Exercise 2.2

A certain sum amounts to ₹ 798.60 after 3 years and ₹ 878.46 after 4 years. Find the interest rate and

the sum.

It is given that

Amount after 3 years = ₹ 798.60

Amount after 4 years = ₹ 878.46

So the difference = 878.46 – 798.60 = ₹ 79.86

Here ₹ 79.86 is the interest on ₹ 798.60 for 1 year.

We know that

Rate = (SI × 100)/ (P × t)

Substituting the values

= (79.86 × 100)/ (798.60 × 1)

Multiply and divide by 100

= (7986 × 100 × 100)/ (79860 × 100 × 1)

= 10%

Here

By further calculation

P = 79860/100 × 10/11 × 10/11 × 10/11

P = ₹ 600

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