1st) Write the numbers from left to right:
………. 10 14 20
[The periods: …… are just to indent the lines. They have no mathematical meaning.]
2nd) If possible, rip out a factor common to all numbers. The factor 2 is common. So divide the three numbers by 2 [10 ÷ 2 = 5 and 20 ÷ 2 = 10] and show the result below:
2 | 10 14 20
………. 5 7 10
3rd) At this point, notice there’s no number that
goes into the remaining numbers: 5, 7, 10. That means you’ve found that
the GCF is the number pulled out, 2. At this point we’re at a
crossroads. We’re done finding the GCF, but now we’re at the start of a
new process, finding the LCM.
To proceed toward getting the LCM, see if there’s any number that goes into any pair of remaining numbers. Well, 5 goes into 5 and 10. So divide both those numbers by 5 [5 ÷ 5 = 1 and 10 ÷ 5 = 2] , and show the results below:
2 | 10 14 20
5 | 5 7 10
……….. 1 7 2
Notice that if there’s a number 5 doesn’t go into, you leave that number as is. So leave the 7 as 7.
4th) Repeat. See if there’s a number that goes into
two of the remaining numbers. Since nothing goes into 1, 7, and 2,
we’re done. To get the LCM, multiply all of the outer numbers. That
means you multiply the numbers you pulled out on the left (2 and 5), and
also multiply the numbers at the bottom (1, 7 and 2). Ignoring the
meaningless 1, you have: 2 x 5 x 7 x 2 = 140, and that’s the LCM.Hope this helps!!
