baizea

Learning target:

Use the prime factorization of composit numbers to recognize the least common multiple.(LCM)

Examples:

       1.  25=5•5     12=2•2•3    Because there are no common factors,

         /\            /\             you multiply all the factors to get the

        5•5          6•2             LCM.

                      /\               2•2•3•5•5=300

                     3•2               LCM=300

       2.  18=3•3•2     20=5•2•2      Because there are common factors,

            /\              /\                for each of the common factors (2, 5, and 3)

           9•2            5•4                count the amount there are for each  

          /\                 /\                number, and take the ones with the most for each factor

         3•3               2•2                and only multiply those.

                                                  Take,2,2,3,3, and 5.  2•2•3•3•5=180   LCM=180

Lesson:

If the numbers have no common factors, multiply all the prime factors.  If the numbers do have common factors, for each of the common factors count the amount of the common prime factors from each number, then take the ones with the most for each factor, and only multiply those.

Take a self check quiz on using prime factorization to find the LCM.