Ladder Method for LCM
I can find the Least Common Multiple
Vocabulary
LCM (Least Common Multiple): the smallest # that is a multiple of 2 or
more given #’s.
Steps
1). Create a table like the one to the right; writing the
two numbers whose LCM you are to find in the upper
right hand boxes (A & B).
2). Think of a number that will go into both of those
numbers and write it in the upper left hand box.
20
48
(A)
2
20
(C)
(B)
48
(A)
(B)
2 goes into 20 and
2 also goes into 48
3). Divide the # in Box A by the # in Box C and write the
quotient in the box below A.
2
(C)
20
48
(A)
(B)
20  2 =
10
4). Divide the # in Box B by the # in Box C and write the
quotient in the box below B.
2
(C)
20
10
5). Is there a # that will go into both 10 & 24? Yes. 2
will. Create a new row below the bottom row and repeat
the process.
2 will go into 10 & 24
6). Divide 10 by 2 and 24 by 2. Write the quotients below
each #.
2
(C)
20
(B)
48  2 =
24
48
(A)
(B)
2
10
24
2
20
48
(C)
2
7). Is there a # that will go into both 5 & 12? NO
48
(A)
(A)
(B)
10
24
10  2 =
24  2 =
5
12
8). The LCM is found by multiplying the numbers in the left hand column
and the bottom row. It forms an “L” for LCM.
2 x 2 x 5 x 12 = 240
so the LCM of 20 & 48 is 240
Revised 1/10/17