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Saturday, 31 October

JEE Main 2025 · MathsMultiple choiceSingle correctEasyCalculation

JEE Main 2 April 2025, Shift 2, Maths Q9

Question 9 of 75 in this shift, Maths question 9 of 25, Section A.

Given three indentical bags each containing 10 balls, whose colours are as follows : Bag I: Red 3, Blue 2, Green 5 Bag II: Red 4, Blue 3, Green 3 Bag III: Red 5, Blue 1, Green 4 A person chooses a bag at random and takes out a ball. If the ball is Red, the probability that it is from bag I is pp and if the ball is Green, the probability that it is from bag III is qq, then the value of (1p+1q)\left(\frac{1}{p}+\frac{1}{q}\right) is :

The figure, in words

Table of ball colours per bag: Bag I (Red 3, Blue 2, Green 5), Bag II (Red 4, Blue 3, Green 3), Bag III (Red 5, Blue 1, Green 4).
  1. (1)88
  2. (2)66
  3. (3)77Official answer
  4. (4)99

Official answer

Option 3

NTA final key.

Chapter
Probability
Topic
Bayes' Theorem
Idea tested
Bayes' Theorem Application

Same idea in other shifts

Asked 9× in all
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  7. 24 Jun 2022, Shift 1 · Q4Bag A contains 2 white, 1 black and 3 red balls and bag B contains 3 black, 2 red and n white balls. One bag is chosen at random and 2…MediumSingle correct
  8. 25 Feb 2021, Shift 2 · Q75In a group of 400 people, 160 are smokers and non-vegetarian; 100 are smokers and vegetarian and the remaining 140 are non-smokers and…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. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.