GCF and LCM · part 7 of 7
Practice Problems
Thirteen of them, with a hint, a next step and the answer on each.
Practice: try it, then get help one step at a time
Try each one yourself first. Hint gets you a nudge from Finn, Show next step walks it one step at a time, Reveal answer checks, and Hide help / start over clears the card. Draw the line-up every time, even when you think you can see the answer.
Finn
Two checks you can always do yourself. The GCF has to divide into both numbers. The LCM has to have both numbers divide into it. If one of those fails, something slipped in the line-up.
My results
Finished the practice? Print a page that shows each question, what you typed or chose, the correct answer, and how it went. Good for showing a teacher or keeping in a folder.
Exit ticket
On paper. Use the words, not just the numbers.
- Say what "greatest common factor" is asking for, in your own words, without using the words greatest, common or factor.
- Find the GCF and the LCM of 20 and 50. Draw the line-up.
- Why can the LCM never be smaller than the bigger of your two numbers?
- Which one would you use to reduce 2050, and which one to add 120 + 150?
Check your exit ticket
- Something like: the biggest number that divides evenly into both of them.
- 20 = 2 x 2 x 5 and 50 = 2 x 5 x 5. Pairs: one 2 and one 5. Leftovers: a 2 from 20 and a 5 from 50. GCF = 2 x 5 = 10. LCM = 2 x 5 x 2 x 5 = 100. Check: 100 ÷ 20 = 5 and 100 ÷ 50 = 2.
- Because a multiple of a number is never smaller than that number. The LCM is a multiple of both, so it has to be at least as big as the bigger one.
- The GCF, 10, reduces 2050 to 25. The LCM, 100, is the common denominator: 5100 + 2100 = 7100.