JEE Main 2019 — Binomial Theorem Question with Solution
From: JEE Main 2019 (Online) 9th April Evening Slot
Question
If some three consecutive in the binomial
expansion of (x + 1)n is powers of x are in the ratio
2 : 15 : 70, then the average of these three
coefficient is :-
Choose an option
Show full solutionCorrect option: D
Correct answer
D232
Step-by-step explanation
Given
.... (i)
Now
14r + 14 = 3n – 3r
17r = 3n – 14 ... (ii)
Now From (i) and (ii) equation
2n + 2 = 3n - 14 n = 16
By putting n = 16 in equation (i)
r = 2
Average of coefficient =
=
=
.... (i)
Now
14r + 14 = 3n – 3r
17r = 3n – 14 ... (ii)
Now From (i) and (ii) equation
2n + 2 = 3n - 14 n = 16
By putting n = 16 in equation (i)
r = 2
Average of coefficient =
=
=
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This is a previous-year question from JEE Main 2019, covering the Binomial Theorem chapter of Mathematics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.