LCM for 20 and 21

The first method to find LCM for numbers 20 and 21 is to find Greatest Common Factor (GCF) of these numbers. Here's the formula:

LCM = (Number1 × Number2) ÷ GCF

GCF of numbers 20 and 21 is 1, so

LCM = (20 × 21) ÷ 1

LCM = 420 ÷ 1

LCM = 420

The second method to find LCM for numbers 20 and 21 is to list out the common multiples for both nubmers and pick the first which matching:

Multiples of 20: 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, 420, 440, 460

Multiples of 21: 21, 42, 63, 84, 105, 126, 147, 168, 189, 210, 231, 252, 273, 294, 315, 336, 357, 378, 399, 420, 441, 462

So the LCM for 20 and 21 is 420

Another method to find LCM for numbers 20 and 21 is to list all Prime Factors for both numbers and multiply the highest exponent prime factors: