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Option 1 : 7 years
GIVEN:
Principal = Rs. 75000
SI = Rs. 87750
CONCEPT:
Simple interest concept.
Cumulative rate if the rate of interest is ‘R1’ for ‘T1’ years and ‘R2’ for ‘T2’ years = R1T1 + R2T2
FORMULA USED:
SI = PRT/100
Where P = Principal, R = rate of interest, T = Time
CALCULATION:
Suppose the rate was 15% for ‘t’ years.
So,
Cumulative rate = 15 × t + 18 × 4 = (15t + 72)%
Now,
/100 = 87750
⇒ (15t + 72) = 117
⇒ 15t = 45
⇒ t = 3
Hence,
Total time of investment = 3 + 4 = 7 years
∴ the time for which the sum is invested for the varying rate of Interest = 7 years.
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