Question:
A man deposited Rs 10000 in a bank at the rate of $5 \%$ simple interest annually. Find the amount in $15^{\text {th }}$ year since he deposited the amount and also calculate the total amount after 20 years.
Solution:
It is given that the man deposited Rs 10000 in a bank at the rate of 5% simple interest annually.
$\therefore$ Interest in first year $=\frac{5}{100} \times$ Rs $10000=$ Rs 500
$\therefore$ Amount in $15^{\text {th }}$ year $=\mathrm{Rs} 10000+\underbrace{500+500+\ldots .+500}_{14 \text { times }}$
= Rs 10000 + 14 × Rs 500
= Rs 10000 + Rs 7000
= Rs 17000
Amount after 20 years $=$ Rs $10000+\underbrace{500+500+\ldots .+500}_{20 \text { times }}$
= Rs 10000 + 20 × Rs 500
= Rs 10000 + Rs 10000
= Rs 20000