I don not understand how to do least common mutiples.

Can I please get some help.

I need to find the least common multiple of 420 and 196.

there is a real neat way to do this which works for the LCM of any number of numerals.

420 196
-------| divide each number by a common factor
105 49 | 4
15...7.} 7

there are no more common factors
so the LCM is the multiplation of the numbers on the far right as well as the last row
so LCM = 4 x 7 x 15 x 7 2940

if you had more than 3 numbers to start with there was a common factor for only some of them, take it out until there is no common factor for any

e.g.

400 250 230

200 125 215 | 2
40..25 43...| 5
8....5 43...| 5

so LCM = 2x5x5x8x5x43

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