Question
An amount was invested at a simple interest rate. After 6
years, it amounted to (126/108) times the amount it had reached in 4 years. What is the rate of interest per annum?Solution
ATQ,
Let the rate of interest be ‘r%’ p.a.
Let the amount after 4 years = Rs. ‘108x’
So, amount after 6 years = (126/108) × 108x = Rs. ‘126x’
Interest in 2 years = 126x – 108x = Rs. ‘18x’
So, yearly interest = 18x / 2 = Rs. ‘9x’
Principal = 108x – 9x × 4 = Rs. ‘72x’
ATQ,
72x × (r / 100) × 1 = 9x
r = (9x × 100) / 72x = 12.5
The rate of interest = r = 12.5%
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