Prime Numbers are those that are only divisible by one and the number itself. They include, but are not limited to, 1, 2, 3, 5, 7, 11, 13, 17, 23, 29, 31, 37, 41, 43, and 47. Notice that the only even number that is a prime number is the number 2.
To find prime factors use a factor tree like the ones below. Begin with the first prime number that will divide evenly into the number to be factored.
To find the lowest common multiple, multiply the terms in both sets, but do not use duplicated terms. If a term appears in both factor sets, use the factors with the greatest exponent.
To find the greatest common factor, only use the factors that appear in both sets. If a number is duplicated, use the duplicated factor with the smallest exponent. The prime number 2 appears in both the factoring of 80 and 90, but in the factoring of 80, 2 has an exponent of 4 and of 90, 2 has an exponent of 1. There is only one 2 in 90, so you must use the 2. However, 5 appears only once in factoring both numbers.
The GCF is