LCM for 18 and 21

The first method to find LCM for numbers 18 and 21 is to find Greatest Common Factor (GCF) of these numbers. Here's the formula:

LCM = (Number1 × Number2) ÷ GCF

GCF of numbers 18 and 21 is 3, so

LCM = (18 × 21) ÷ 3

LCM = 378 ÷ 3

LCM = 126

The second method to find LCM for numbers 18 and 21 is to list out the common multiples for both nubmers and pick the first which matching:

Multiples of 18: 18, 36, 54, 72, 90, 108, 126, 144, 162

Multiples of 21: 21, 42, 63, 84, 105, 126, 147, 168

So the LCM for 18 and 21 is 126

Another method to find LCM for numbers 18 and 21 is to list all Prime Factors for both numbers and multiply the highest exponent prime factors: