Question

the compound interest of rupees 20000 at 10% per annum compounded annually for a certain period of time is rupees 4200 find the time

Answer 1

CI=A+[1+R/100]TO THE POWER N WHERE N IS= NUMBER OF TIME
20000=4200+(1+10/100)n
20000-4200=15800
1+10/100=110/100 after showing smallest form=
11/10

Answer 2

Answer:

The time period of the compound interest = 17 years

Step-by-step explanation:

Principal = Rs. 20000

Rate = 10%

Interest is compounded annually so n = 1

Compound Interest = Rs 4200

$\text{Compound Interest = }Principal\times (1+\frac{rate}{n\times 100})^{n\times time}\\\\4200=20000(1+\frac{10}{100})^{time}\\\\0.21=1.1^{time} \\\implies time=\frac{\log0.21}{\log1.1}\\\\\implies time=17\text{ years}$

Hence, the time period of the compound interest = 17 years