Learn

Saturday, 31 October

JEE Main 2021 · MathsMultiple choiceSingle correctMediumCalculation

JEE Main 25 July 2021, Shift 2, Maths Q70

Question 70 of 90 in this shift, Maths question 10 of 30, Section A.

Let X be a random variable such that the probability function of a distribution is given by P(X=0)=12P(X=0)=\frac{1}{2}, P(X=j)=13jP(X=j)=\frac{1}{3^j} (j=1,2,3,.....,∞)(j=1,2,3,.....,\infty) Then the mean of the distribution and P(X is positive and even) respectively are :
  1. (1)34\frac{3}{4} and 18\frac{1}{8}Official answer
  2. (2)34\frac{3}{4} and 116\frac{1}{16}
  3. (3)38\frac{3}{8} and 18\frac{1}{8}
  4. (4)34\frac{3}{4} and 19\frac{1}{9}

Official answer

Option 1

NTA final key.

Same idea in other shifts

Asked 2× in all
  1. 8 Apr 2023, Shift 2 · Q17If the probability that the random variable XX takes values xx is given by P(X=x)=k(x+1)3−xP(X = x) = k(x + 1)3^{-x}, x=0,1,2,3,…x = 0, 1, 2, 3, \ldots, where…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.