Question

Gollum eats fish on alternate days.How often doea he eat fish on a Monday?

Answer 1

Given that a week has 7 days, that makes it an odd number of days.

If Gollum eats fish on alternate days, then he will be able to have fish on alternate Mondays. (i.e. he eats on on one Monday, he will miss the next Monday, then he gets to eat again the following Monday) 

Answer: He gets to have fish on alternate Mondays.

Answer 2

He eats fish every other Monday