RRB NTPC - Averages (200 Questions with Explanation): Quantitative Aptitude Test

1.

There were 45 students in a hostel, if the numbers of students increased by 7, the expenses of the mess were increased by Rs. 39 per day while the average expenditure per head diminished by Re.1. What is the original expenditure of the mess (in Rs)?

   A.) 562
   B.) 585
   C.) 548
   D.) 650

Answer: Option 'B'

Let the original expenditure be Rs.x
Original average expenditure = X/45
New average expenditure = (x+39)/52
So (x/45) - ((x+39) / 52) = 1 => (52x - 45x - 45 × 39) / (45 × 52) = 1 => (7x - 1755) / 2340 = 1 => 7x = 2340 + 1755 => 7x = 4095 so x = 585
so, original expenditure is Rs 585

2.

The average age of a group of 10 students was 18. The average age increased by 1 years when two new students joined the group. What is the average age of the two new students who joined the group?

   A.) 15.5
   B.) 12.5
   C.) 24
   D.) 16.5

Answer: Option 'C'

The average age of a group of 10 students is 18.
Therefore, the sum of the ages of all 10 of them = 10 * 18 = 180
When two students joins the group, the average increase by 1.
New Average = 19 Now there are 12 students Therefore, sum of all the ages of 12 students = 228
Therefore, the sum of the ages of two students who joined = 228 - 180 = 48
And the average age of these two students = 24

3.

In a class of 27, the overall weight of the students is 997. Can you find the average weight of students in the class? 

   A.) 36.93
   B.) 38.78
   C.) 40.62
   D.) 35.08

Answer: Option 'A'

Use the below formula to find the average weight of the class
Average Weight = (Total Weight of Class / Total Number of Students)
=>Average Weight = (997/27) = 36.93

4.

The average of 26 numbers is zero. Of them, at the most how many may be greater than zero?

   A.) 25
   B.) 27
   C.) 24
   D.) 13

Answer: Option 'A'

Average of 26 numbers is = 0 Therefore sum of all 26 numbers = 0
It is quite possible that 25 of these numbers may be positive and if their sum is "a" then 26th number is "(-a)"

5.

The average age of father and his two sons is 27 Years. Five years ago, the average age of the two sons was 12 Years. If the difference between the ages of the two sons is four years, what is the present age of the father? 

   A.) 42
   B.) 47
   C.) 48
   D.) 49

Answer: Option 'B'

The total present age of father and two sons is 3S27 = 81 yrs
The total present age of sons is (12+5) X 2 = 34Years
so, present age of father is 81 - 34 = 47 yrs

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