Challenge Level

Choose four different digits from 1-9 and put one in each box so that the resulting four two-digit numbers add to a total of 100.

Challenge Level

Can you arrange the numbers 1 to 17 in a row so that each adjacent pair adds up to a square number?

Challenge Level

Can you picture how to order the cards to reproduce Charlie's card trick for yourself?

Challenge Level

How many solutions can you find to this sum? Each of the different letters stands for a different number.

Challenge Level

The clues for this Sudoku are the product of the numbers in adjacent squares.

Challenge Level

Five numbers added together in pairs produce: 0, 2, 4, 4, 6, 8, 9, 11, 13, 15 What are the five numbers?