You can use cross products to determine if the ratios are equivalent.
Yes.
Practice makes perfect
To determine if the given ratios form a proportion. Let's first write them as fractions.
ccc
Ratio & & Fraction [0.8em]
1to 3 & → & 1/3 [1em]
7to 21 & → & 7/21
Then, we will set them equal to one another and use the Cross Products Property. If the resulting equation is true, then the ratios form a proportion.