Question
An amount becomes Rs. 11,520 after 3 years at a simple
interest rate of r% p.a. If the rate had been increased to (r + 5)% per annum, the same sum would become Rs. 12,570 in 3 years. Calculate the original sum invested.Solution
ATQ,
Let the sum invested be Rs. ‘P’.
Simple interest at r% = 11520 – P
So, 11520 – P = P × 3 × r ÷ 100
Or, 100 × (11520 – P) = 3Pr ………. (I)
Simple interest at (r + 5)% = 12570 – P
So, 12570 – P = P × (r + 5) × 3 ÷ 100
Or, 100 × (12570 – P) = 3Pr + 15P ………. (II)
From (I) and (II),
1257000 – 100P = 1152000 – 85P
Or, 105000 = 15P
P = 7000
Therefore, sum = Rs. 7,000
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