Question

The mean of the following frequency distribution is 43.75 :
Class 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100
Frequency 8 4 20 45 64 32 f 8 2 2
Find the missing frequency f.

Answer 1

Solution :-

Class Fi Xi FiXi

0-10 8 5 40

10-20 4 15 60

20-30 20 25 500

30-40 45 35 1575

40-50 64 45 2880

50-60 32 55 1760

60-70 f 65 65f

70-80 8 75 600

80-90 2 85 170

90-100 2 95 190

⅀Fi=185+f ⅀FiXi=7775+65f

we know that,

• Mean = ⅀FiXi / ⅀Fi

so,

→ (7775 + 65f) /(185 + f) = 43.75

→ 7775 + 65f = 8093.75 + 43.75f

→ 65f - 43.75f = 8093.75 - 7775

→ 21.25f = 318.75

→ f = (318.75/21.25)

→ f = 15 .(Ans.)

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