Three different recipes each make a different number of cookies and require a different amount of flour.

Recipe 1: 1 dozen cookies; 1 cup of flour
Recipe 2: 3 dozen cookies; 3.5 cups of flour
Recipe 3: 5 dozen cookies; 6 cups of flour

Determine if the three recipes use a proportional amount of flour.

Yes, it is proportional because the ratios between the number of cookies and cups of flour are all equivalent.
Yes, it is proportional because the cookies increase by 2 dozen for every 2.5 cups of flour.
No, it is not proportional because the ratios between the number of cookies and cups of flour are not all equivalent.
No, it is not proportional because the number of cookies and cups of flour could not be zero at the same time.