Classifying Numbers by Their Properties
Primary 4 · Mathematics
Classifying Numbers by Their Properties
Lesson 5 of 5
30 min
Let's begin
At a bus park, a bus to Muhanga leaves every 4 minutes and a bus to Rwamagana leaves every 6 minutes. At 7:00 both buses leave together. Habimana wonders: when will they next leave at the same time?
List the multiples of each number and look for numbers that are in both lists. These are common multiples. The smallest one is the lowest common multiple (LCM).
The LCM of 4 and 6 is 12. So the two buses next leave together 12 minutes later, at 7:12.
Uwase has 12 avocados and 18 bananas. She wants to pack them into bags that are all the same, with nothing left over. What is the greatest number of bags she can make?
The common factors are 1, 2, 3 and 6. The biggest one is the greatest common factor (GCF): 6.
Uwase can make 6 bags. Each bag has 12 ÷ 6 = 2 avocados and 18 ÷ 6 = 3 bananas.
Tip
Multiples meet later, factors share now. The LCM is at least as big as the bigger number. The GCF is never bigger than the smaller number.
Work each one in your exercise book first. Then tap Show answer to check.
Find the LCM of 3 and 5.
Answer: 15
Find the LCM of 6 and 8.
Answer: 24. Multiples of 8: 8, 16, 24. 24 is the first one that is also a multiple of 6.
Find the GCF of 15 and 25.
Answer: 5
Find the GCF of 8 and 12.
Answer: 4
One light blinks every 3 seconds and another every 4 seconds. They blink together now. After how many seconds will they next blink together?
Answer: 12 seconds (the LCM of 3 and 4)
What you learned today
Sources and credits
The stories, Rwandan worked examples, diagrams and practice questions were written by Ganzaa.
Quick check
What is the LCM of 4 and 10?
