Free practice on LCM, HCF, Factors and Multiples for Class 6, following the Cameroon primary school curriculum (English subsystem). Every answer is explained, so a parent who is not sure of the answer can still help.
Break each number into primes, then multiply the SHARED primes. HCF of 24 and 36: 24 = 2·2·2·3; 36 = 2·2·3·3. Shared: 2·2·3 = 12. So HCF = 12.
LCM = Lowest Common Multiple. Take all primes with the HIGHEST power in either. 24 = 2³·3; 36 = 2²·3². Highest of each: 2³·3² = 8·9 = 72. LCM = 72.
A cool rule: for any two numbers, HCF × LCM = the two numbers multiplied. Check: 24 × 36 = 864, and HCF (12) × LCM (72) = 864. ✓
| a | b | HCF | LCM | HCF×LCM = a×b |
|---|---|---|---|---|
| 6 | 8 | 2 | 24 | 48 |
| 12 | 18 | 6 | 36 | 216 |
| 24 | 36 | 12 | 72 | 864 |
What is the LCM of 6 and 8?
Write your answer, then check below.
Answer: 24
Multiples of 6: 6,12,18,24… Multiples of 8: 8,16,24… Lowest common = 24.
What is the LCM of 4 and 10?
Write your answer, then check below.
Answer: 20
What is the HCF of 24 and 36?
Write your answer, then check below.
Answer: 12
12 is the biggest number that divides both 24 and 36 exactly.
All the factors of 18 are:
Answer: A. 1, 2, 3, 6, 9, 18
Two church bells ring every 6 minutes and every 9 minutes. They ring together now. After how many minutes will they ring together again?
Answer: B. 18
LCM of 6 and 9 = 18 minutes.
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