[tex]28:2=14\\14:2=7\\7:7=1\\\\28=\boxed{2}\cdot2\cdot7\\\\30:2=15\\15:3=5\\5:5=1\\\\30=\boxed{2}\cdot3\cdot5\\\\Answer:\ GCF(28,\ 30)=\boxed{2}[/tex]
Other method:
Factors of 28: 1, 2, 4, 7, 14, 28
Factors of 30: 1, 2, 3, 5, 6, 10, 15, 30
GCF(28, 30) = 2
