There exists a grassy field that contains no other food. 11 goats could last there for 7 days before they run out of food. 10 goats could last 8 days there. How long could 3 goats survive there?
I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UKhere and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.