Estimating BIG Number Multiplication

This game is based on noughts and crosses, but can be played by 2 or 3 players. Instead of a blank 3 by 3 grid, draw up a grid of 6 by 6 squares and write into them (in a random order) the numbers: 70, 110, 130, 140, 160, 190, 210, 220, 260, 290, 300, 320, 370, 380, 420, 460, 470, 480, 530, 560, 610, 660, 680, 700, 750, 820, 830, 850, 940, 970, 1050, 1110 and 1250.

There will be 3 blank squares so you will need to repeat three of the numbers to ensure there are no spaces left in your grid.

At the top of your piece of paper, write in nice big letters with a circle around them the following numbers: 18, 32, 53, 76, 94, 117 and 139. Underneath write in the same size letters, but with a star around each of them 4, 6, 7, 8 and 9.

A calculator is used in this game, but only for the actual multiplication. Players take turns at choosing a number from a circle and a digit from a star. Once they’ve chosen their numbers, they may use the calculator to multiply their two numbers together. They place their counter on the square in the grid that contains the answer to their multiplication (rounded to the nearest 10). The first to get three of their counters in a row is the winner (same as noughts and crosses).

It is an excellent game for estimation because of the rounding after the calculation, and the fact that children will soon become very skilled at estimating the answer to the multiplication BEFORE they choose their numbers. Telling them they can use the calculator to do the multiplication often gives more confidence because they think they won’t have to do maths, but they soon find that the calculator is more an arbitrator/checker than a tool to help them win the game. If you are playing in pairs, the calculator bit can be done by the other person.

For more challenge, make the grid bigger and let the child choose ANY of the numbers to multiply instead of restricting it to a “circle x star” combination. Get them to work out what numbers you will need to add to your grid for the game to still work.