The sum of each column and row in this grid give the totals as shown. What number goes in the starred square?

Weekly Problem 21 - 2010

How many diagonals can you draw on this square...

In the multiplication table on the right, only some of the numbers have been given. What is the value of A+B+C+D+E?

Four cards have a number on one side and a phrase on the back. On each card, the number does not have the property described on the back. What do the four cards have on them?

What is the smallest number of jelly babies Tom must take, to be certain that he gets at least one of each flavour?

Two of the numbers in a 4x4 magic square have been swapped. Can you work out the sum of these numbers?

Can you work out the sum of the missing digits in this subtraction?

What is the largest number Sophie can use to have seven positive integers with a mean of 7?

Can you place the nine cards onto a 3x3 grid such that every row, column and diagonal has a product of 1?

Each interior angle of a particular polygon is an obtuse angle which is a whole number of degrees. What is the greatest number of sides the polygon could have?

In a 7-digit numerical code, each group of four consecutive digits adds to 16, and each group of five consecutive digits adds to 19. What is the sum of all 7 digits?

Can you make the numbers around each face of this solid add up to the same total?