posted by ferrer .
LCM of 4 and 20 is 2 or 4. Which one?
GCF for 11 and 31 is 1?
GCF for 14 and 21 is 7?
The least common multiple is a number that both numbers can divide evenly. It's at least as large as the largest of the pair of numbers. Therefore the LCM of 4 and 20 is NOT 2 or 4.
Your other two answers are correct.