Question

if rs 8000 amount to rs 9861 in 3 years compound interest,find the rate of interest per annum.​

Answer 1

Answer:

amount 7081 he 9863 in 6 year compund interest

Answer 2

Correct Question:

If Rs. 8000 amount to Rs. 9261 in 3 years compound interest, Find the rate of interest per annum.

9861 is not a perfect cube, so we can't find the value of R exactly. Also, if we solve reversely above solution, we get the time 3 years but with 9861 we can't get 3 years so 9261 is the correct.

Given:

✰ Principal ( P ) = Rs. 8000

✰ Amount ( A ) = Rs. 9261

✰ Time ( n ) = 3 years

To find:

✠ Rate ( r )

Solution:

✰ Principal ( P ) = Rs. 8000

✰ Amount ( A ) = Rs. 9261

Interest = Amount - Principle

➙ Interest = 9261 - 8000

➙ Interest = Rs. 1261

Now,

✰ Time ( n ) = 3 years

Using formula

A = P[ 1 + ( r/100 ) ]ⁿ

Putting the values in,

• 9261 = 8000[ 1 + ( r/100 ) ]³

• 9261/8000 = [ 1 + ( r/100 ) ]³

• (21)³/(20)³ = [ 1 + ( r/100 ) ]³

• (21/20)³ = [ 1 + ( r/100 ) ]³

• 21/20 = 1 + ( r/100 )

• (21/20) -1 = r/100

• (21-20)/20 = r/100

• 1/20 = r/100

• 20r = 100

• r = 100/20

• r = 5

∴ The rate of interest = 5%

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