Bunuel wrote:
Set A contains 120 terms with an average of 8.2. Set B contains 240 terms with an average of 10.6. If Set A and B are combined what is the resulting average?
(A) 8.4
(B) 8.8
(C) 9.0
(D) 9.8
(E) 10.1
Weighted average = (120*8.2 + 240*10.6) / 120 +240
=984+ 2544 / 360
=3528/360 = 9.8
The above method is calculation intensive.
Alternatively ,
Set A has 120 terms with average 8.2
Set B has 240 terms with average 10.6
Difference between average of set A and B = 2.4
Number of terms of B : Number of terms of A = 2:1
2x+x = 2.4
=> x = .8
So the weighted average will be in opposite ratio of relative weights
8.2+ 2*.8 = 9.8
Answer D
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