Average (Railway Maths) (Part – II)

Total Questions: 50

21. The mean of ages of 9 children in a joint family is 14 years. The ages of their grandfather and grandmother are 71 years and 67 years respectively. Find the mean of the ages of children and grandparents. [RRB NTPC 09/01/2021 (Morning)]

Correct Answer: (b) 25 years
Solution:

22. The mean of ages of a group of 35 school students is 16 years. A 52 year old teacher joined the group. Find the mean of the ages of the students and the teacher. [RRB NTPC 11/01/2021 (Evening)]

Correct Answer: (d) 17 years
Solution:

23. If the sum of five consecutive numbers is 90, then what is the middle number? [RRB NTPC 11/01/2021 (Evening)]

Correct Answer: (c) 18
Solution:

24. If the speeds of a train in 10 successive hours are a₁, a₂, a₃, a₄, a₅, a₆, a₇, a₈, a₉ and a₁₀, then the average speed of the train is: [RRB NTPC 13/01/2021 (Morning)]

Correct Answer: (d) arithmetic mean of a₁, a₂, a₃, a₄, a₅, a₆, a₇, a₈, a₉ and a₁₀
Solution:

The average speed of the train is the arithmetic mean of all speeds.

25. As of this year, the average age of a family of 8 members is 39 years. Assuming that after six years the family adopts a new-born baby, what will be the average age of the family 10 years from now? [RRB NTPC 16/01/2021 (Evening)]

Correct Answer: (c) 44 years
Solution:

26. A rainfall of 0.896 cm was recorded in 7 h. What was the average amount of rain per hour? [RRB NTPC 19/01/2021 (Morning) ]

Correct Answer: (c) 0.128 cm
Solution:

27. The mean of 100 observations is 50. If one observation 50 is replaced by 150, then what will be the new mean? [RRB NTPC 19/01/2021 (Evening)]

Correct Answer: (b) 51
Solution:

28. The mean of 25 observations is 36. If the mean of its first 13 observations is 32 and the mean of the last 13 observations is 40, then what will be its 13th observation? [RRB NTPC 19/01/2021 (Evening)]

Correct Answer: (b) 36
Solution:

29. The mean of the first eight odd natural numbers is: [RRB NTPC 20/01/2021 (Morning)]

Correct Answer: (c) 8
Solution:

30. The average weight of an apple in a sample of 10 apples was calculated as 104 g. Later on, it was found that the weighing had shown the weight of each apple 20 g less. The correct average weight of an apple in that sample is: [RRB NTPC 20/01/2021 (Morning)]

Correct Answer: (d) 124 g
Solution: