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Using the ready reckoner, find the period of interest for an amount equal to Rs 16,939.2, when the principal is Rs 12000 at 9% p.a.

Last updated date: 27th Mar 2023
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Hint: Find the compound interest using the amount and principal for R = 9%. Then find the compound interest for Re1. By using the ready reckoner table find the value corresponding to compound interest at 9%.

Complete step-by-step answer:
Ready Reckoner is a pre-calculated table of interest for different amounts and internal rates.
Acquired Interest per Rupee, compounded yearly,


From the question, we have been given the Amount, principal and rate of interest.

Amount, A = 16939.2
Principal, P = Rs 12000
Rate of interest, r = 9%
First we need to find the compound interest.
Compound interest is the addition of interest to the principal sum of a loan or deposit, or in other words interest on interest.
\[\Rightarrow \]Compound interest = Amount – Principal = A – P
                                        = 16939.2 – 12000 = 4939.2 Rupees.
Thus we have Rs. 4939.2 as compound interest for the principal of Rs. 12000 at 9%.
Now we need to find the compound interest for Re.1.
For Rs 12000, the compound interest is Rs 4939.2.
Therefore, for Principal Re.1, the compound interest \[=\dfrac{4939.2}{12000}=0.4116\]
Now from the ready reckoner, find the year corresponding to the compound interest 0.4116.
From the table you will get the value as 4.
Therefore, the period of interest, n = 4.

Note: The ready reckoner table is available for different rates of interest.
But for this problem on the value corresponding to the rate of interest 9% is required.
The ready reckoner table can be used to facilitate simple calculations, especially for applying the rates of discount, interest, charging etc.