JEE Main 2020 · MathsMultiple choiceSingle correctMediumMulti-step

JEE Main 6 September 2020, Shift 2, Maths Q56

Question 56 of 75 in this shift, Maths question 6 of 25.

The common difference of the A.P.

b_1, b_2, \ldots, b_m

is 2 more than the common difference of A.P.

a_1, a_2, \ldots, a_n

. If

a_{40}=-159

a_{100}=-399

and

b_{100}=a_{70}

, then

b_1

is equal to :

(1) $81$
(2) $-81$ Official answer
(3) $127$
(4) $-127$

Official answer

Option 2

NTA final key (Sep 2020).

Chapter: Sequences and Series
Topic: AP and GP
Idea tested: AP General Term

Same idea in other shifts

Asked 7× in all

2 Apr 2026, Shift 2 · Q4Let $a_1, a_2, a_3, \ldots$ be an A.P. and $g_1, g_2, g_3, \ldots$ be an increasing G.P. If $a_1 = a_2 + g_2 = 1$ and $a_3 + g_3 = 4$ ,…MediumSingle correct
5 Apr 2026, Shift 2 · Q6Let $A_1, A_2, A_3, \dots\dots, A_{39}$ be 39 arithmetic means between the numbers 59 and 159. Then the mean of $A_{25}, A_{28}, A_{31}$ …EasySingle correct
25 Jul 2022, Shift 1 · Q24Let $a,\ b$ be two non-zero real numbers. If $p$ and $r$ are the roots of the equation $x^2-8ax+2a=0$ and $q$ and $s$ are the roots of the…HardNumerical value
27 Jun 2022, Shift 2 · Q6If $a_1, a_2, a_3\,......$ and $b_1, b_2, b_3......$ are A.P., and $a_1=2,\ a_{10}=3,\ a_1b_1=1=a_{10}b_{10}$ , then $a_4\,b_4$ is equal to -MediumSingle correct
3 Aug 2021, Shift 1 · Q86Let $f(x) = x + 1$ and $g$ be maps on $\mathbb{R}$ and $h(n) = (g \circ f)(n+1) - (g \circ f)(n)$ , $n \in \mathbb{N}$ . Further,…HardNumerical value
4 Sep 2020, Shift 2 · Q57Let $a_1, a_2, \ldots, a_n$ be a given A.P. whose common difference is an integer and $S_n = a_1 + a_2 + \ldots + a_n$ . If…MediumSingle correct

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.