Farmer Bob owns a piece of grassland and three animals: a cow, a goat, and a goose. Bob discovered the following:

• When the cow and the goat graze in the field together, there is no more grass after 45 days.
• When the cow and the goose graze in the field together, there is no more grass after 60 days.
• When the cow grazes in the field alone, there is no more grass after 90 days.
• When the goat and the goose graze in the field together, there is also no more grass after 90 days.

The question: How long can the three animals graze in the field together?

A hint : Click here!

The solution: Click here!