Club X and Club Y

[Bek]

How many members are in both Club X and Club Y?

(1) There were 15 members at the joint conference for members of Club X and Club Y, and no members were absent.

(2) Club X has 6 members and Club Y has 12 members.


OA: C


I don't understand why A) is incorrect answer. Question asks the total # of members in both clubs.


source: grockit.com

[shankar.ashwin]

From (1) you know, there are a total of 15 people, but we dont know how many were a part of both X and Y (intersection)
From (2) we know n(x)=6 and n(y)=12, but we still dont know how many were part of both.

Together we know, n(x U y) = n(x) + n(y) - N(XY)

We need to find n(XY) = n(x) + n(y) - n(x U Y) = 6+12-15 = 3

Hence c

[fcabanski]

Another way to solve it is with a Venn Diagram.