Mathematics · Probability

JEE Main 2026 — 2 April, Evening Shift — Question 30

A man throws a fair coin repeatedly. He gets 10 points for each head he throws and 5 points for each tail he throws. If the probability that he gets exactly 30 points is mn\frac{\mathrm{m}}{\mathrm{n}}, gcd(m,n)=1\mathrm{gcd}(\mathrm{m},\mathrm{n}) = 1, then m+n\mathrm{m} + \mathrm{n} is equal to :

  1. Option A:

    53

  2. Option B:

    55

  3. Option C:

    107

    Correct
  4. Option D:

    105

Answer: C

Step-by-step solution

P=(6\mathrm{P}=(6 tail )+(4)+(4 tail +1 head )+(2)+(2 tail +2 head )+(3)+(3 head )) P=(12)6+5!1!4!(12)5+4!2!2!(12)4+(12)3\mathrm{P}=\left(\frac{1}{2}\right)^{6}+\frac{5!}{1!4!}\left(\frac{1}{2}\right)^{5}+\frac{4!}{2!2!}\left(\frac{1}{2}\right)^{4}+\left(\frac{1}{2}\right)^{3} P=164+532+38+18\mathrm{P}=\frac{1}{64}+\frac{5}{32}+\frac{3}{8}+\frac{1}{8} P=1+10+24+864=4364=mn\mathrm{P}=\frac{1+10+24+8}{64}=\frac{43}{64}=\frac{\mathrm{m}}{\mathrm{n}} m+n=107\mathrm{m}+\mathrm{n}=107

Answer key and solution verified before publishing.

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Exam
JEE Main 2026
Subject
Mathematics
Chapter
Probability
Topic
Introduction to Probability