In mathematics, a factor pair is two whole numbers which when multiplied together produce another number. While 2, 3, 5 and 6 are all factors of 30, only 5 and 6 are a factor pair, because 2 and 3 have 15 and 10 as their factor pairs. By definition, every factor must belong to at least one factor pair. Sometimes, the factor pair is two of the same number! (For example: 3, 3 is a factor pair of 9, since 3x3 = 9.)