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ch1´╝ÜFactor: an integer is divided by another integer, which is the former factors such as 1, 2, 4 are factor multiple of 8: a number can be divided by another number, this number is another number times as 15 can Is divisible by 3 or 5, so 15 is a multiple of 3 and a multiple of 5. Prime number: a number in addition to 1 and its own no other factor, called the prime number. Such as 2, 3, 5, 7, and the number: a number in addition to 1 and its own and other factors, (at least three factors) called the composite. Such as 4,6,8,9 neither composite nor a prime factor: a number of their common factor, called the common factor, such as, 12 and 6 of the common factors are: 1,2,3,6 common multiple: a number The number of their common factor, called the common multiple. For example, the common multiples of 3 and 6 are: 3, 6, 12, 18, . . . . . The factor of a number is finite, and the multiple is infinite. The largest common factor: the number of the largest number of their common one. The greatest common divisors, such as 6 and 12, are 6 the most common multiple: the number of which is the smallest of their common divisors. The basic properties of the fraction: When the numerator and the denominator simultaneously expand or shrink the same multiple, the fractional value does not change. The basic nature of the decimal: the end of the decimal add 0 or remove the 0, the decimal size is not1