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Ahmad recorded the lengths, in minutes, of the 150 phone calls he made one month.
His results are summarised in the table.
0
5
Length of
callſt
minutes)
Frequency
35
42
30
28
15
Calculate an estimate of the mean length of a call.
Answers
Answer:
C.I 130−139 140−149 150−159 160−169 170−179 180−189 190−199
Frequency 4 9 18 28 24 10 7
Now we can prepare a table or calculating median
C.I Continous C.I Frequency Cumulative frequency(cf)
130−139 129.5−139.5 4 4
140−149 139.5−149.5 9 4+9=13
150−159 149.5−159.5 18 13+18=31cf
160−169 159.5−169.5 28(f) 31+28=59
170−179 169.5−179.5 24 59+24=83
180−189 179.5−189.5 10 83+10=93
190−199 189.5−199.5 7 93+7=100
Here
N=100
⇒N/2=
2
100
=50
30 median class 159.5−169.5
Because the cf(59) is near to (50)
∴ Lower limit of median
Class(l)=159.5
Class width(h)=10,
cf=preceding cf of median class
f=frequency of median class
∴ Median=l+(
f
N/2−cf
)×h
=159.5+(
28
50−31
)×10
=159.5+
28
19
×10
=159.5+
28
190
=159.5+6.786
(Rounded to one decimal)
Median=166.286≅166.3.