LCM — Grade 6 Math, what it means and where it is taught
Least common multiple — the smallest number both divide into.
Taught in Grade 6 Math.
Where it is taught
What it rests on
Work through these first if this one does not settle.
- Multiple — The result of multiplying by a whole number: 12 is a multiple of 4.
Practise this idea
9 questions in the course bank use LCM, in GCF and LCM. The first 8 are below; the rest are in those units.
Problem 1
Find the LCM of 4 and 6.
Worked answer
12
Multiples of 6: 6, 12, …
12 is the first also divisible by 4.
Problem 2
Find the LCM of 5 and 7.
Worked answer
35
5 and 7 are relatively prime
LCM = 5 × 7 = 35
Problem 3
Find the LCM of 12 and 18.
Worked answer
36
12 = 22 · 3, 18 = 2 · 32
Highest powers: 22 · 32 = 36
Problem 4
Find the LCM of 8 and 12.
Worked answer
24
Highest powers: 23 · 3
= 24
Problem 5
Two lighthouses flash every 12 and 18 seconds, together right now. After how many seconds do they next flash together?
Worked answer
36
LCM of 12 and 18
22 · 32 = 36 seconds
Problem 6
Two numbers have GCF 6 and LCM 90. One of them is 18. Find the other.
Worked answer
30
6 × 90 = 540
540 ÷ 18 = 30
Check: GCF(18, 30) = 6 ✓
Problem 7
Find the LCM of 15, 20 and 25.
Worked answer
300
15 = 3 · 5, 20 = 22 · 5, 25 = 52
Highest powers: 22 · 3 · 52
= 4 × 3 × 25 = 300
Problem 8
Two numbers have GCF 8 and LCM 48. One is 16. Find the other.
Worked answer
24
8 × 48 = 384
384 ÷ 16 = 24