addition rule of probability - Wikitechy https://www.wikitechy.com/interview-questions/tag/addition-rule-of-probability/ Interview Questions Mon, 06 Sep 2021 05:49:03 +0000 en-US hourly 1 https://wordpress.org/?v=6.9 https://www.wikitechy.com/interview-questions/wp-content/uploads/2025/10/cropped-wikitechy-icon-32x32.png addition rule of probability - Wikitechy https://www.wikitechy.com/interview-questions/tag/addition-rule-of-probability/ 32 32 A brother and sister appear for an interview against two vacant posts in an office. The probability of the brother’s selection is 1/5th and that of the sister’s selections is 1/3rd. What is the probability that one of them is selected ? https://www.wikitechy.com/interview-questions/probability/a-brother-and-sister-appear-for-an-interview-against-two-vacant-posts-in-an-office-the-probability-of-the-brothers-selection-is-1-5th-and-that-of-the-sisters-selections-is-1-3rd-what-is-the-prob/ https://www.wikitechy.com/interview-questions/probability/a-brother-and-sister-appear-for-an-interview-against-two-vacant-posts-in-an-office-the-probability-of-the-brothers-selection-is-1-5th-and-that-of-the-sisters-selections-is-1-3rd-what-is-the-prob/#respond Wed, 18 Aug 2021 02:10:04 +0000 https://www.wikitechy.com/interview-questions/?p=2051

A brother and sister appear for an interview against two vacant posts in an office. The probability of the brother’s selection is 1/5th and that of the sister’s selections is 1/3rd. What is the probability that one of them is selected ?

A. 1/5

B. 2/5

C. 1/3

D. 2/3

Answer : B. 2/5

Explanation:

Probability that only one of them is selected = (prob. that brother is selected) × (prob. that sister is not selected) + (Prob. that brother is not selected) × (Prob. that sister is selected)

Hence, Required Probability = 1/5 x 2/3 + 4/5 x 1/3
= 2/15 + 4/15
= 6/15
= 2/5.

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