Answer:
The way I would best say is listing all the multiples then circle all the ones that are alike then find the lowest one they all have.
Example
Find the common multiples of 12,15,20
Multiples of 12:12, 24, 36, 48, 60, 72, 84, 96, 120……….
Multiples of 15:15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165, 180, 195, 210, 225, 240, 255, 270, 285, 300, 315, 330, 345, 360, 375, 390, 405,……..
Multiples of 20:20, 40, 60, 80, 100, 120, 140, 160, 180, and 200.
Explanation:
They all have 60 so your lcm is 60