To find the number of chew toys Rex has, we need to set up the equation based on the information given. Rex has half as many chew toys as Snoopy, who has 12 chew toys.
We can express this relationship with the equation:
\( r = \frac{1}{2} \times 12 \)
Substituting the value of Snoopy's toys into the equation gives:
\( r = 12 \div 2 \)
Thus, the one-variable, one-step equation is:
r = 12 / 2
So, you should fill in the blank with the division symbol (/) to show that Rex has half of Snoopy's chew toys.