Probability (Railway Maths)

Total Questions: 29

1. In a chess tournament, there are 125 participants. The game will be played on a knock-out basis. How many matches are to be played in the entire tournament? [NTPC CBT - I 27/01/2021 (Evening) ]

Correct Answer: (a) 124
Solution:

No. of matches played = 125 - 1 = 124.

2. If 9 students are standing on a circular path, then the probability that 2 of them are always standing together is. [NTPC CBT - I 17/02/2021 (Morning) ]

Correct Answer: (a) 1/4
Solution:

3. ‘n’ number of persons stand on the circumference of a circle at distinct points. Each possible pair of persons, not standing next to each other, sings a two minute song. One pair after the other. If the total time taken for singing is 40 minutes, then what is the value of ‘n’? [NTPC CBT - I 14/03/2021 (Evening) ]

Correct Answer: (b) Eight
Solution:

4. A bag contains balls numbered 1, 2, 3, ………. 30. One ball is drawn from the bag at random. What is the probability that the number on the ball drawn is divisible by 4 or 6? [NTPC CBT - I 06/04/2021 (Evening) ]

Correct Answer: (b) 1/3
Solution:

5. If ⁿC₄ = 70, then find n. [NTPC CBT - I 31/07/2021 (Morning) ]

Correct Answer: (b) 8
Solution:

6. A box contains 3 black and 4 red balls. Another box contains 2 black and 3 red balls. The balls taken out of these boxes are mixed together and placed in a third box. Now two balls are selected at random from the third box. Find the probability that one ball is black and the other is red? [ALP Tier II 21/01/2019 (Afternoon) ]

Correct Answer: (a) 35/66
Solution:

7. Two dice are thrown simultaneously and the sum of the numbers appearing on them is noted. What is the probability that the sum is 12? [RRB NTPC 30/12/2020 (Morning)]

Correct Answer: (c) 1/36
Solution:

8. A box contains 6 white, 2 black and 3 red balls. If a ball is drawn at random, what is the probability that it will not be white. [RRB NTPC 09/01/2021 (Morning)]

Correct Answer: (c) 5/11
Solution:

9. A box contains 6 white balls and 7 black balls. Two balls are drawn at random. What is the probability that both of them are of different colours? [RRB NTPC 22/02/2021 (Evening)]

Correct Answer: (d) 7/13
Solution:

10. Two letters selected from the word ‘TENDULKAR’. The probability that both are vowels is: [RRB NTPC 22/02/2021 (Evening) ]

Correct Answer: (b) 1/12
Solution: