Choose either the beginning or advanced grid for Factor Captor. The beginning grid has fewer numbers and is best for teaching new players the rules, while the advanced grid should be used for students who have already mastered the beginning grid.
Place a marker of some kind on a two-digit number. For example, if the first player chooses 20, she will have 20 points added to her total. The second player would then put a marker on all of the factors of 20: 2, 4, 5 and 10. The second player's initial score is the total of these numbers, or 21, giving him more points than the first player. If the second player misses a factor, such as by forgetting that 4 is a factor of 20, the first player can place a marker on that missed factor and add it to her own total.
Play Factor Captor until all the numbers have been covered, keeping track of the score along the way. The player with the highest total when all of the numbers have been covered is the winner.