How do you find the LCM of 15, 20?

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Answer 1 · 2016-11-28T14:34:41

60

method 1

write out the multiples of both numbers until the lowest common one id found

multiples 15: $" "{15,30, 45,color(blue)60,75,90,105,color(blue)120,135,...}$

multiples 20: $" "{20,40,color(blue)60, 80,100,color(blue)120,...}$

$LCM(15,20)=60$

method 2

use $hcfxxlcm=axxb$

$hcf=gcm(15,20)=5$

so $" "5xxlcm=15xx20$

$lcm=(15xx20)/5$

cancel before evaluating makes it easier.

$lcm=(cancel(15)^3xx20)/cancel(5)=60$