Down at the maths pond, four frogs each sit on a pentagonal lily pad. Two red frogs with triangular eyes are sitting on one side and two yellow frogs with lozenge-shaped eyes sit on the other. There is one lily pad between them.
One day the frogs decide to swap sides. However, the law of the land says that frogs must abide by four rules: (1) frogs can only move one at a time, (2) there can only be one frog on a lily pad at any time, (3) frogs can slide on to the adjacent lily pad and (4) frogs can only jump over one frog forwards or backwards.
What is the least number of moves it takes for the frogs to change sides?
The frog puzzle is a delightful challenge to inspire problem solving and planning ahead. Children take the place of the frogs and chairs become lily pads. The rest of the class can call out and tell which frog to move. You can then build up to three, four, five, six or seven frogs on each side.
The problem can be extended by having an unequal number of frogs on each side or having two spare lily pads in between
John Dabell teaches at Lawn Primary School in Derby.