# Examples(Set 3) - Average

11. A family consists of two grandparents, two parents and three grandchildren. The average age of the grandparents is
67
years, that of the parents is
35
years and that of the grandchildren is
6
years. What is the average age of the family in years?

A.222/7

B.221/7

C.220/7

D.219/7

Explanation:

Total age of grandparents = 67 × 2

Total age of parents = 35 × 2

Total age of grandchildren = 6 × 3

Total age of all persons = 67 × 2 + 35 × 2 + 6 × 3 = 222

Total number of persons = 2 + 2 + 3 = 7 = 7

Average age of the family = 222/ 7

12. The average weight of Advay, Bharat and Chiku is
45
kg. If the average weight of Advay and Bharat be
40
kg and that of Bharat and Chiku be
43
kg, what is the weight of Bharat?

A.
28.5
kg

B.
31
kg

C.
32
kg

D.
30.5
kg

Explanation:

Total weight of Advay+Bharat+Chiku = 45 × 3 = 135

Total weight of Advay+Bharat = 40 × 2 = 80

Therefore, weight of Chiku = 135 − 80 = 55

Total weight of Bharat+Chiku = 43 × 2 = 86

Hence weight of Bharat = 86 − 55 = 31

13. If the average marks of three batches of
55
,
60
and
45
students respectively is
50
,
55
,
60
,
what is the average marks of all the students?

A.
50

B.
51.33

C.
53.23

D.
54.68

Explanation:

Required average = (55 × 50 + 60 × 55 + 45 × 60)/ (55 + 60 + 45)

= 54.68

14. The average age of husband, wife and their child
3
years ago was
27
years and that of wife and the child
5
years ago was
20
years. What is the present age of the husband?

A.
28

B.
30

C.
40

D.
32

Explanation:

average age of husband ,wife and child 3 years ago=27

sum of ages of husband ,wife and child 3 years ago=27x3

present sum of ages of husband ,wife and child =(27+3)x3=90

average age of wife and child 5 years ago=20

sum of ages of wife and child 5 years ago=20x2

present sum of ages of wife and child =(20+5)x2=50

present sum of ages of husband=90-50

=40

15. The average weight of
8
persons increases by
2.5
kg when a new person comes in place of one of them weighing
65
kg. What is the weight of the new person?

A.
50
kg

B.
85
kg

C.
80
kg

D.
75
kg

Explanation:

Let weight of new person be x

Total increase in weight = 8 × 2.5 = 20

⇒ x − 65 = 20

⇒ x = 85