JEE Main 2018 — Sequences And Series Question with Solution
From: JEE Main 2018 (Online) 15th April Evening Slot
Question
Let An = . . . . . + (1)n-1 and Bn = 1 An.
Then, the least dd natural numbr p, so that Bn > An , for all n p, is :
Then, the least dd natural numbr p, so that Bn > An , for all n p, is :
Choose an option
Show full solutionCorrect option: B
Correct answer
B7
Step-by-step explanation
An =
Which in a G.P. with a = , r = and number of terms = n
An =
An = . . . . . . . . . .(1)
As, Bn = 1 An
For least odd natural number p, such that Bn > An
1 An > An 1 > 2 An An <
From eqn. (1), we get
1
1 <
As n is odd, then =
So < >
log = n log 6.228 < n
Hence, n should be 7.
Which in a G.P. with a = , r = and number of terms = n
An =
An = . . . . . . . . . .(1)
As, Bn = 1 An
For least odd natural number p, such that Bn > An
1 An > An 1 > 2 An An <
From eqn. (1), we get
1
1 <
As n is odd, then =
So < >
log = n log 6.228 < n
Hence, n should be 7.
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This is a previous-year question from JEE Main 2018, covering the Sequences And Series 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.