Answer:
GCF 4, LCM 80
Step-by-step explanation:
Since both 16 and 20 have two 2s as factor, their greatest common factor is 4.
The LCM is found by multiplying all of the remaining factors by the LCM:
16 still has (2 x 2), 20 still has (5), times the GCF (4) so 2 x 2 x 5 x 4 = 80.
