A certain sum amounts to ₹ 798.60 after 3 years and ₹ 878.46 after 4 years. Find the interest rate and the sum.
Solution:
It is given that
Amount after 3 years = ₹ 798.60
Amount after 4 years = ₹ 878.46
So the difference = 878.46 – 798.60 = ₹ 79.86
Here ₹ 79.86 is the interest on ₹ 798.60 for 1 year.
We know that
Rate = (SI × 100)/ (P × t)
Substituting the values
= (79.86 × 100)/ (798.60 × 1)
Multiply and divide by 100
= (7986 × 100 × 100)/ (79860 × 100 × 1)
= 10%
Here
A = P (1 + r/100)n
It can be written as
P = A ÷ (1 + r/100)n
Substituting the values
P = 798.60 ÷ (1 + 10/100)3
By further calculation
P = 79860/100 × 10/11 × 10/11 × 10/11
P = ₹ 600
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