Aptitude question and answer on Average

In this section we are going to discuss about average problems. Not just the overview of the topic, but also you are going to learn the important formulas on average along with explanation which is easy to understand.

17
The average salary per month of 30 employees in INFINITY LTD. is Rs. 4000.If the manager's salary is added, the average salary increases to Rs. 4300, What is the salary of the manager ?
A.    Rs. 13500
B.    Rs. 12500
C.    Rs. 12300
D.    Rs. 13300

Answer : D.  Rs. 13300

Explanation:
Salary of the manager = Rs.\((31 \times4300-30\times4000)\)

                                =Rs.13300.

18
Find the average of all prime numbers between 30 and 50?
A.    60.8
B.    59.8
C.    49.8
D.    39.8

Answer : D.  39.8

Explanation:
There are five prime numbers between 30 and 50.

They are 31,37,41,43 and 47.

Therefore the required average=\((31+37+41+43+47) \over5\)

=> \(199 \over 5\)

=> 39.8

 

19
find the average of first 40 natural numbers?
A.    20.5
B.    21.6
C.    26.8
D.    20.9

Answer : A.  20.5

Explanation:
sum  of first n natural numbers=\(n(n+1) \over2\)

So,sum of 40 natural numbers=\((40 \times41) \over 2\)= 820.

Therefore  the required average=\({820 \over 40}\)=20.5.
 

20
find the average of first 20 multiples of 7 ?
A.    63.15
B.    73.5
C.    63.5
D.    83.5

Answer : B.   73.5

Explanation:
Required average =\(7(1+2+3+...........+20) \over20\)
By usingh below formula
\(1 + 2 + 3 + \cdots + n=\sum{n}= \dfrac{n(n+1)}{2}\)
We will get 

=> \((7 \times20 \times21) \over20 \times2\)=\(147 \over 2\)= 73.5.

21
The average of four consecutive even numbers is 27. find the largest of these numbers ?
A.    30
B.    31
C.    32
D.    33

Answer : A.  30

Explanation:
Let the numbers be \(x,x+2,x+4 \) and \(x+6. \)
then,
\({(x+(x+2)+(x+4)+(x+6)) \over4 }= 27\) 

\(=> {(4x+12) \over4 } = 27\)

\(x+3=27\)

\(x=24.\)

Therefore the largest number=(x+6)=24+6=30.
 

22
There are two sections A and B of a class consisting of 36 and 44 students respectively. If the average weight of section A is 40kg and that of section B is 35kg, find the average weight of the whole class ?
A.    35.25 kg
B.    36.25 kg
C.    37.25 kg
D.    38.25kg

Answer : C.  37.25 kg

Explanation:
Total weight of (36+44) students=\((36 \times40+44 \times35)kg\)  =2980kg.

Therefore average weight of the whole class=\(2980 \over80\)kg  =37.25kg.
 



23
Nine persons went to a hotel for taking their meals 8 of them spent Rs.12 each on their meals and the ninth spent Rs.8 more than the average expenditure of all the nine.What was the total money spent by them ?
A.    116
B.    117
C.    118
D.    119

Answer : B.   117

Explanation:
Let the average expenditure of all nine be Rs.x

Then \(12 \times8+(x+8)=9x\) or   \(8x=104\) or \(x=13\).

Total money spent = 9x=Rs. \(9 \times 13\)=Rs.117.
 

24
Of the three numbers, second is twice the first and is also thrice the third.If the average of the three numbers is 44.Find the largest number.
A.    70
B.    71
C.    72
D.    73

Answer : C.  72

Explanation:
Let the third number be x.

Then second number = 3x.

First number=\(3x \over2\).

Therefore \(x+3x+ \bigg({3x \over2 } \bigg)\)=\((44 \times3)\) or x=24

So largest number= 2nd number=3x=72.