₹1,380 has to be paid after 4 years. If four equal instalments are required with a simple interest of 10% on each instalment, then what is the value of each instalment?

Let each equal annual installment be ₹x.
The total amount due after 4 years is the sum of the installments plus the interest accrued on them until the end of the 4 years.

First installment is paid at the end of year 1, so it accumulates interest for 3 years: x+
100
x×10×3
​
=1.3x

Second installment accumulates interest for 2 years: x+
100
x×10×2
​
=1.2x

Third installment accumulates interest for 1 year: x+
100
x×10×1
​
=1.1x

Fourth installment is paid at the end of year 4, so it accumulates no interest: x

Summing these up gives the total debt of ₹1,380:

1.3x+1.2x+1.1x+x=1380
4.6x=1380
x=
4.6
1380
​
=300
Thus, each instalment is ₹300.