Question: In how many years Rs 8,000 amounts to Rs 9,621 at 5% p.a. compound interest?


Solution:
Given,

Principal amount (P) = Rs 8,000
Amount (A) = Rs 9,621
Rate of compound interest (R) = 5% p.a.

To find: time (T) = ?

We know,

$Amount = P \left ( 1 + \dfrac{R}{100}  \right )^T$

$or, 9621 = 8000 \left ( 1 + \dfrac{5}{100} \right )^T$

$or, \dfrac{9621}{8000} = \left ( 1 + \dfrac{1}{20} \right )^T$

$or, \dfrac{21^3}{20^3} = \left ( \dfrac{20+1}{20} \right )^T$

$or, \left ( \dfrac{21}{20} \right )^3 = \left ( \dfrac{21}{20} \right )^T$

$or, 3 = T$

$\therefore T = 3 years$

Therefore, the required time for the principal RS 8,000 to amount RS 9,621 at 5% p.a. compound interest is 3 years.

Related Notes and Solutions:

Here is the website link to the notes of Indices.

Here is the website link to the notes of Compound Interest.

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