JEE Main 2026 · 2 Apr · Shift 1 · Mathematics Q8

MathematicsSingle correct+4 / -1Question 8 of 75

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 :

2x^2-23x-10=0

4x^2-35x+24=0

2x^2-19x-10=0

2x^2-35x+98=0

Answer and worked solution

Official answer: C

Class marks 7.5, 12.5, 17.5, 22.5, 27.5, 32.5.

Sums. $\sum f=90+2k$ and $\sum fx=15+12.5k+490+1215+27.5(k+1)+162.5=1910+40k$ .

Mean. $\dfrac{1910+40k}{90+2k}=21$ gives $1910+40k=1890+42k$ , so $k=10$ .

Check (C): $2(100)-190-10=0$ ✓.

(C)

Topics:Measures of central tendency

JEE Main 2026 · 2 Apr · Shift 1, Mathematics question 8