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Saturday, 31 October

JEE Main 2022 · MathsMultiple choiceSingle correctHardMulti-step

JEE Main 29 June 2022, Shift 2, Maths Q20

Question 20 of 90 in this shift, Maths question 20 of 30, Section A.

Let n≥5n \geq 5 be an integer. If 9n−8n−1=64α9^n - 8n - 1 = 64\alpha and 6n−5n−1=25β6^n - 5n - 1 = 25\beta, then α−β\alpha - \beta is equal to
  1. (1)1+nC2 (8−5)+nC3 (82−52)+…+nCn (8n−1−5n−1)1 + {}^nC_2\,(8 - 5) + {}^nC_3\,(8^2 - 5^2) + \ldots + {}^nC_n\,(8^{n-1} - 5^{n-1})
  2. (2)1+nC3 (8−5)+nC4 (82−52)+…+nCn (8n−2−5n−2)1 + {}^nC_3\,(8 - 5) + {}^nC_4\,(8^2 - 5^2) + \ldots + {}^nC_n\,(8^{n-2} - 5^{n-2})
  3. (3)nC3 (8−5)+nC4 (82−52)+…+nCn (8n−2−5n−2){}^nC_3\,(8 - 5) + {}^nC_4\,(8^2 - 5^2) + \ldots + {}^nC_n\,(8^{n-2} - 5^{n-2})Official answer
  4. (4)nC4 (8−5)+nC5 (82−52)+…+nCn (8n−3−5n−3){}^nC_4\,(8 - 5) + {}^nC_5\,(8^2 - 5^2) + \ldots + {}^nC_n\,(8^{n-3} - 5^{n-3})

Official answer

Option 3

NTA final key.

Topic
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Idea tested
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Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.