Question

2 3 1
7
Find the average of 65,5--4- and 7
5' 4' 5 10
1
1
1
2.
(c) 4.
80
(d) 7
80
8080
Find the average of 20 20
(a) 5-1
(b) 6
10​

Answer 1

Answer:

Correct option is

D

8,12

Class

Frequency(f)

ClassMark (x)

fx

0-20

5

10

50

20-40

f

1

30

30f

1

40-60

10

50

500

60-80

f

2

70

70f

2

80-100

7

90

630

100-120

8

110

880

Total

30+f

1

+f

2

2060+30f

1

+70f

2

Given 30+f

1

+f

2

=50

=>f

1

+f

2

=20 -- (1)

Given, Mean =

∑f

∑fx

=62.8

=>

30+f

1

+f

2

2060+30f

1

+70f

2

=62.8

=>2060+30f

1

+70f

2

=1884+62.8f

1

+62.8f

2

32.8f

1

−7.2f

2

=176

=> 8.2f

1

−1.8f

2

=44

=> 4.1f

1

−0.9f

2

=22 -- (2)

Solving both equations 1, 2, we get

f

1

=8,f

2

=12