This is a problem solving lesson with 11 challenges which get harder as the numbers progress. Children have one challenge at a time, which is sheet with a hundred square on and several clues, mostly relating to multiples, odd,evens, greater than and less than. They have to work out the mystery number. How many can they do in a given time? When I did this lesson the children really enjoyed it. They can cross off numbers on the h/sq as they read the clues.