Norrie sees two lights flash at the same time, then one of them flashes every 4th second, and the other flashes every 5th second. How many times do they flash together during a whole minute?
Can you score 100 by throwing rings on this board? Is there more than way to do it?
In this 100 square, look at the green square which contains the numbers 2, 3, 12 and 13. What is the sum of the numbers that are diagonally opposite each other? What do you notice?
Place this "worm" on the 100 square and find the total of the four squares it covers. Keeping its head in the same place, what other totals can you make?
This 100 square jigsaw is written in code. It starts with 1 and ends with 100. Can you build it up?
Choose any three by three square of dates on a calendar page...