Club X and Club Y

BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

This topic has expert replies

Post new topic Post Reply

Previous Topic Next Topic

Bek: Senior | Next Rank: 100 Posts; Posts: 68; Joined: Fri Dec 03, 2010 10:29 pm; Thanked: 5 times; Followed by:1 members

Club X and Club Y

by Bek » Fri Oct 07, 2011 10:20 pm

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

Quote

Source: Beat The GMAT — Data Sufficiency | Fri Oct 07, 2011 10:20 pm

shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 am; Thanked: 230 times; Followed by:21 members

by shankar.ashwin » Fri Oct 07, 2011 10:26 pm

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