JEE Main 2025 · MathsMultiple choiceSingle correctMediumCalculation

JEE Main 7 April 2025, Shift 2, Maths Q10

Question 10 of 75 in this shift, Maths question 10 of 25, Section A.

A bag contains 19 unbiased coins and one coin with head on both sides. One coin drawn at random is tossed and head turns up. If the probability that the drawn coin was unbiased, is

\frac{m}{n}

\gcd(m,n)=1

, then

n^2-m^2

is equal to :

(1)60
(2)64
(3)72
(4)80Official answer

Official answer

Option 4

NTA final key.

Chapter: Probability
Topic: Bayes' Theorem
Idea tested: Biased vs Unbiased Instrument Selection

Same topic in other shifts

All Bayes' Theorem questions

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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.