Brain Play is a collection of mathematical puzzles meant to stretch your logical and numerical reasoning. Playing with these puzzles is a great way to make friends with math!
Puzzles are posted periodically here, each followed by a solution. Print-friendly versions of all problems and solutions to date can be found here.
Happy puzzling!
→ Print-friendly version Eventually you want to be in a position where there is only 1 pebble left and it’s the troll’s turn. That means if there are 2 pebbles left and it’s your turn, you should take away 1; and if there are 3 pebbles left, you should take 2. In those cases you can force the troll to take the last pebble.
On the other hand, you don’t want to have 4 pebbles left when it’s your turn, because after your turn there will be 2 or 3 pebbles left and the troll will be able to make you take the last pebble.
→ Print-friendly version Farmer Brown can’t take the wolf across first, since then the goat would be left behind with the lettuce, and we know what goats do to lettuce. Similarly, he can’t take the lettuce across first, since then the wolf would be left behind with the goat. But wolves don’t eat lettuce, so he takes the goat across first.
Next, he rows back alone, and then rows the wolf across.
