Answer
a) $2r^{2}$
b) 5
Work Step by Step
Factors of $2r^{3}$ : 1 $\times$ 2 $\times$ r $\times$ r $\times$ r
Factors of $12r^{2}$ : 3 $\times$ 2 $\times$ 2 $\times$ r $\times$ r
a) They both have a 2 $\times$ r $\times$ r common, thus the greatest common factor of $2r^{3}$, $12r^{2}$, is $2r^{2}$
Factors of $5r$ : 5 $\times$ r
Factors of 30: 2 $\times$ 3 $\times$ 5
b) They both have a 5 common thus the greatest common factor of 5r and 30 is 5
