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JEE Main 20268 AprilEvening Shift
Exam
JEE Main
Year
2026
Date
8 April
Shift
Evening Shift
Subject
Mathematics
Chapter
Probability

JEE Main 2026 · 8 April · Evening Shift · Mathematics · Probability

A candidate has to go to the examination centre to appear in an...

A candidate has to go to the examination centre to appear in an examination. The candidate uses only one means of transportation for the entire distance out of bus, scooter and car. The probabilities of the candidate going by bus, scooter and car, respectively, are 25\dfrac{2}{5}, 15\dfrac{1}{5} and 25\dfrac{2}{5}. The probabilities that the candidate reaches late at the examination centre are 15\dfrac{1}{5}, 13\dfrac{1}{3} and 14\dfrac{1}{4} if the candidate uses bus, scooter and car, respectively. Given that the candidate reached late at the examination centre, the probability that the candidate travelled by bus is:

Options

  1. A1137\dfrac{11}{37}
  2. B1237\dfrac{12}{37}
  3. C1337\dfrac{13}{37}
  4. D1437\dfrac{14}{37}

Correct answer

B. 1237\dfrac{12}{37}

Step-by-step solution

Let E1E_1, E2E_2, and E3E_3 be the events that the candidate travels by bus, scooter, and car, respectively.

The probabilities of choosing these modes of transport are:
P(E1)=25P(E_1) = \dfrac{2}{5}
P(E2)=15P(E_2) = \dfrac{1}{5}
P(E3)=25P(E_3) = \dfrac{2}{5}

Let AA be the event that the candidate reaches the examination centre late. The conditional probabilities of reaching late are:
P(A∣E1)=15P(A|E_1) = \dfrac{1}{5}
P(A∣E2)=13P(A|E_2) = \dfrac{1}{3}
P(A∣E3)=14P(A|E_3) = \dfrac{1}{4}

We need to find the probability that the candidate travelled by bus given that they reached late, which is P(E1∣A)P(E_1|A).

Using Bayes' theorem:
P(E1∣A)=P(E1)P(A∣E1)P(E1)P(A∣E1)+P(E2)P(A∣E2)+P(E3)P(A∣E3)P(E_1|A) = \dfrac{P(E_1)P(A|E_1)}{P(E_1)P(A|E_1) + P(E_2)P(A|E_2) + P(E_3)P(A|E_3)}

Substituting the given values:
P(E1∣A)=25×15(25×15)+(15×13)+(25×14)P(E_1|A) = \dfrac{\dfrac{2}{5} \times \dfrac{1}{5}}{\left(\dfrac{2}{5} \times \dfrac{1}{5}\right) + \left(\dfrac{1}{5} \times \dfrac{1}{3}\right) + \left(\dfrac{2}{5} \times \dfrac{1}{4}\right)}

P(E1∣A)=225225+115+110P(E_1|A) = \dfrac{\dfrac{2}{25}}{\dfrac{2}{25} + \dfrac{1}{15} + \dfrac{1}{10}}

Taking the LCM of the denominators 2525, 1515, and 1010, which is 150150:
P(E1∣A)=1215012150+10150+15150P(E_1|A) = \dfrac{\dfrac{12}{150}}{\dfrac{12}{150} + \dfrac{10}{150} + \dfrac{15}{150}}

P(E1∣A)=1212+10+15=1237P(E_1|A) = \dfrac{12}{12 + 10 + 15} = \dfrac{12}{37}

Answer: 1237\dfrac{12}{37}
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