A bachelor spends one half of his salary on entertainment,one fifth on food,one tenth on clothes and one fifth on rent.What fraction of his salary is left?

Answer 1

Not really geometry, but:
1/2 + 1/5 + 1/10 + 1/5 = 1
The bachelor has no money left, or 0/1 left.

Answer 2

1.0 - (0.5 + 0.2 + 0.1 + 0.2) = 0

Answer 3

mmmh,
I guess that explains why he is still a bachelor