CA Foundation · Quantitative Aptitude · Sequence and Series
Ramesh repays a loan in monthly instalments forming an AP. The first instalment is ₹2,000 and each later instalment is ₹150 more than the previous one. If he pays 20 instalments, what is the total amount repaid?
The total repaid is ₹68,500. Using the AP sum formula with a = 2,000, d = 150 and n = 20, S = 10 × (4,000 + 19×150) = 10 × 6,850 = ₹68,500. The final instalment is ₹4,850, confirming the average of ₹3,425 per instalment.
- A₹68,500Correct
- B₹70,000
- C₹62,000
- D₹66,500
Explanation
S20 = 20/2 × [2×2000 + 19×150] = 10 × (4000 + 2850) = 10 × 6850 = ₹68,500. Check: the last instalment is 2000 + 2850 = 4850, and the average of 2000 and 4850 is 3425, so 20 × 3425 = 68,500. The value ₹66,500 arises from using 18 differences instead of 19.
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