A farmer owns a cow, a goat and a goose.
She decides to go on holidays. 
She must insure that the grass field can feed her three animals during her absence.

Information:
- The cow eats as much grass as the goat and the goose. 
- The grass field can feed the cow and goat for 45 days.
- The grass field can feed the cow and goose for 60 days.
- The grass field can feed the goose and goat for 90 days.

Question:
How many days can she leave before her three animals run out of grass?

See answer