Question

Find out the LCM of the following numbers.
(1) 9, 15 (2) 2, 3, 5 (3) 12, 28 (4) 15, 20 (5) 8, 11

Answer 1

(1)
Multiples of 9: 9, 18, 27, 36, 45, 54, 63, 72, 81, 90, 99,...

Multiples of 15: 15, 30, 45, 60,75, 90,...

Common multiples of 9 and 15: 45, 90,...

∴ LCM of 9 and 15 = 45

(2)
Multiples of 2: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30,...

Multiples of 3: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36,...

Multiples of 5: 5, 10, 15, 20, 25, 30, 35,...

Common multiples of 2, 3 and 5: 30, 60, 90,...

∴ LCM of 2, 3 and 5 = 30

(3)
Multiples of 12: 12, 24, 36, 48, 60, 72, 84, 96, 108, 120,...

Multiples of 28: 28, 56, 84, 112,...

Common multiples of 12 and 28: 84, 168,...

∴ LCM of 12 and 28 = 84

(4)
Multiples of 15: 15, 30, 44, 60, 75, 90, 105, 120,...

Multiples of 20: 20, 40, 60, 80, 100, 120,...

Common multiples of 15 and 20: 60, 120,...

∴ LCM of 15 and 20 = 60

(5)
Multiples of 8: 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96,...

Multiples of 11: 11, 22, 33, 44, 55, 66, 77, 88, 99,...

Common multiples of 8 and 11: 88, 176,...

∴ LCM of 8 and 11 = 88