What is the LCM and GCF of 18 and 21?

The least common multiple of 18 and 21 = 126

The smallest positive integer that is divisible by both numbers.

Other names include,

Lowest common multiple = 126

Smallest common multiple = 126

The greatest common factor of 18 and 21 = 3

The Greatest Common Factor is the largest positive integer that will divide into the numbers with zero remainders.

Other names include,

The Greatest Common Divisor (GCD) 18 and 21 = 3

Highest Common Factor (HCF) 18 and 21 = 3

I use a factor tree and a chart in order to find the LCM and the GCF.

Once you have the prime factors for the LCM multiply all the factors together but if you have two of the same factor only use it once.

For the (GCF) find factors that you have pairs of factors.

If you have multiple factors, multiply them together.

If you don't have pairs the (GCF) is 1.

If you have 3 numbers, for the LCM bring down only 1 number if you have two or three numbers in a column, and you must have three numbers in the column for the GCF.

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