Mathematics (NDA SOLVED PAPER 2020 – II) (101 to 120)

Total Questions: 20

11. What is the probability that February of a leap year selected at random, will have five Sundays?

Correct Answer: (b) 1/7
Solution:In a leap year, February has 29 days. In out of 29 days, there are four weeks and one day extra. In out of the four weeks, there exist four Sunday. In one extra days, it may be Sunday or Monday or Tuesday or Wednesday or Thursday or Friday or Saturday. Probability of getting five sundays in the month of February = 1/7

12. The arithmetic mean of 100 observations is 40. Later, it was found that an observation ‘53’ was wrongly read as ‘83’. What is the correct arithmetic mean?

Correct Answer: (b) 39.7
Solution:

13. A husband and wife appear in an interview for two vacancies for the same post. The probability of the husband's selection is 1/7 and that of the wife's selection is 1/5. If the events are independent, then the probability of which one of the following is 11/35?

Correct Answer: (a) At least one of them will be selected
Solution:

14. A dealer has a stock of 15 gold coins out of which 6 are counterfeits. A person randomly picks 4 of the 15 gold coins. What is the probability that all the coins picked will be counterfeits?

Correct Answer: (a) 1/91
Solution:

15. A committee of 3 is to be formed from a group of 2 boys and 2 girls. What is the probability that the committee consists of 2 boys and 1 girl?

Correct Answer: (d) 1/2
Solution:

16. In a lottery of 10 tickets numbered 1 to 10, two tickets are drawn simultaneously. What is the probability that both the tickets drawn have prime numbers?

Correct Answer: (c) 2/15
Solution:

17. Find the value?

Correct Answer: (b) y = 1.12x - 58
Solution:

18. Consider a random variable X which follows Binomial distribution with parameters n = 10 and p = 1/5. Then ,Y = 10 - X follows Binomial distribution with parameters n and p respectively given by

Correct Answer: (d) 10, 4/5
Solution:

19. If A and B are two events such that P(A) = 0.6, P(B) = 0.5 and P( A ∩ B) = 0.4, then consider the following statements

Correct Answer: (d) Neither 1 nor 2
Solution:

20. Three cooks X, Y and Z bake a special kind of cake and with respective probabilities 0.02, 0.03 and 0.05, it fails to rise. In the restaurant where they work, X bakes 50%, Y bakes 30% and Z bakes 20% of cakes. What is the proportion of failures caused by X?

Correct Answer: (b) 10/29
Solution: