Question

The mean of the following frequency table is 50.Frequencies f1 and f2 in classes 20-40 and 60-80 are missing. Find the missing frequencys
Class interval :

0-20 17
20-40 f1
40-60 32
60-80 f2
80-100 19
Total 120

Answer 1

17+32+9+f1+f2=120
=>f1+f2=52 -------(¡)
[(summation)fixi]/[(summation)fi]=50 [GIVEN]
=>[3480+30f1+70f2]/120=50
=>30f1+70f2=(50×120)-3480=2520
=>10 (3f1+7f2)=2520
=>3f1+7f2=252 ---------(ii)
so, now we subtract [equation(i)×3] and [equation(ii)],we get:-
equation(i)×3--- 3f1+3f2= 156
equation (ii)----- +3f1+7f2=+252
(-) (-) (-)
_____________
0-4f2=-96
=>f2=24
Putting the value of f2=24 in equation (i), we get :-
f1+24=52
=>f1=52-24=28

So, f1=28 and f2=24

Answer 2

I hope this will help you