Same chapter3 marksDifficulty: Medium
Find the sum 1 + 3 + 5 + ... + 99.
Arithmetic and Geometric Progression
4 marksDifficulty: Hard
How many terms of the arithmetic progression 9, 17, 25, ... add up to 636?
Original Khojo Papers practice question — not from a past board paper.
Answer
12 terms
No citable source has been recorded for this record. Treat it as practice material, not as fact.
Explanation
With a = 9 and d = 8, Sn = n/2 × [18 + 8(n − 1)] = n(4n + 5). Setting n(4n + 5) = 636 gives 4n2 + 5n − 636 = 0, whose discriminant is 10201 = 1012, so n = (−5 + 101)/8 = 12.
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