Question

51. If total frequencies of three series are 50, 60
and 90 and their means are 12, 15 and 20
respectively, then the mean of their
composite series is
a) 16 b) 15.5
c) 16.5
d) 14.5​

Answer 1

Given frequency = 120

$= > 17 + f1 + 32 + f2 + 19 = 120$

$= > f1 + f2 = 52$

=> Mean

$= 120(10 \times 17) + (30 \times f1) + (50 \times 32) + (72 \times f2) + (90 \times 19)$

=> Mean

$= 120170 + 30f1 + 1600 + 70f2 + 1710 = 50$

$= > 3f1 + 7f2 = 252$

$= > 3f1 + 7(52 - f1) = 252$