If the mean of the data | Class | 5-10 | 10-15 | 15-20 | 20-25 | 25-30 | 30-35 | | Frequency | 2 | $k$ | 28 | 54 | $k+1$ | 5 | is $21$, then $k$ is one of the roots of the equation :

JEE Main 2026 · MathsMultiple choiceSingle correctMediumCalculation

JEE Main 2 April 2026, Shift 1, Maths Q8

Question 8 of 75 in this shift, Maths question 8 of 25, Section A.

If the mean of the data

Class	5-10	10-15	15-20	20-25	25-30	30-35
Frequency	2	$k$	28	54	$k+1$	5

21

, then

k

is one of the roots of the equation :

(1) $2x^2-23x-10=0$
(2) $4x^2-35x+24=0$
(3) $2x^2-19x-10=0$ Official answer
(4) $2x^2-35x+98=0$

Official answer

Option 3

NTA final key.

Chapter: Statistics
Topic: Variance and SD
Idea tested: Mean of Discrete Data

Same idea in other shifts

Asked 4× in all

11 Apr 2023, Shift 1 · Q13Let $x_1, x_2, \ldots, x_{100}$ be in an arithmetic progression, with $x_1 = 2$ and their mean equal to 200. If…MediumSingle correct
18 Mar 2021, Shift 1 · Q87The mean age of 25 teachers in a school is 40 years. A teacher retires at the age of 60 years and a new teacher is appointed in his place.…EasyNumerical value
6 Sep 2020, Shift 2 · Q75Consider the data on $x$ taking the values $0, 2, 4, 8, \ldots, 2^n$ with frequencies ${}^nC_0, {}^nC_1, {}^nC_2, \ldots, {}^nC_n$ …MediumNumerical value

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 42 of the 174 JEE Main shifts held from 2017 to 2026.