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Problem 8 - Entrance Test

The sum of first n terms of an AP is 3n² + 5n. The 10th term is

Correct: A

a₁₀ = S₁₀ - S₉ = (3·10²+5·10)-(3·9²+5·9)=350-252=98. Wait: formula gives 3(100)+50=350; 3(81)+45=288; 350-288=62.