We used this task for sixth graders. The objective was for students to use proportional thinking to reason out which recipe was more concentrated. Students selected one of two solutions in order to state a claim, provide evidence and state a warrant. Many students would find a common denominator in order to demonstrate a higher value ratio of corn syrup to water or total amount (sweeter) or lower value (less sweet). Students might also show how one mixture is sweeter with visual representations such as circles or a drawing of a pitcher with labeled portions.
Microsoft Word version: 6_RP_ProportionalReasoning_Problem_Critique_WhichIsSweeter