Bunuel
If 2/3rds of the members of the Golf Club are also members of the Tennis Club, and 1/2 of the members of the Tennis Club are also members of the Golf Club, what percentage of all people who belong to one or both Clubs belong only to the Golf Club?
A. 5%
B. 10%
C. 15%
D. 20%
E. 75%
This is a question given as an example by
IanStewart several years ago.
Let the no of people in Golf club be \(x\) and that in Tennis club be \(y\)
People who belong to both the club \(= \frac{2x}{3}\)
So people who belong only to golf club \(= x-\frac{2x}{3}=\frac{x}{3}\)
Also half of the Tennis club member belong to both the clubs \(= \frac{y}{2}\)
Hence people who belong only to Tennis club \(= y-\frac{y}{2}=\frac{y}{2}\)
So we have \(\frac{2x}{3}=\frac{y}{2}\)
And total no of people who belong to only one or both the clubs \(= \frac{x}{3}+\frac{y}{2}+\frac{2x}{3}=\frac{x}{3}+\frac{2x}{3}+\frac{2x}{3}=\frac{5x}{3}\)
% who belong only to Golf club \(=\frac{x}{3}/\frac{5x}{3}*100=20\)%
Option
D