A sum of money at simple interest amounts to Rs. 690 in 3 years and to Rs. 720 in 4 years. What is the sum?

Answer 1

Rs. 600

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Simple Interest (SI) for 1 year = 720-690 = Rs. 30
Simple Interest (SI) for 3 years = 30 × 3 = Rs. 90
Principal = 690 - 90 = Rs. 600