The answer is 20. 4 into 20 goes five times and 20 into 20 goes once, of course; so the lowest number that they can both be multiplied into is 20. Try looking at this for help when you need it.
http://www.helpwithfractions.com/least-common-multiple.html
Since 20 is a multiple of 4, it is automatically the LCM.
The LCM is: 60
20
The LCM of 4 and 5 is 20.
The LCM of 4 and 20 is 20
The LCM is 20.
LCM(4, 5, 10) = 20
LCM of 4, 10, and 20 = 20
LCM(4, 5) = 20.
The LCM is 180.
The LCM is 20.
The LCM is 140.