posted by Ella on .
Consider the following students method of solving the proportion 8/5 = 20/x and determine whether the methods were correct: Richie: First I divided 20 by 8 and got 2 1/2. Then I multiplied 2 1/2 by 5 and got 12 1/2 for my answer. Martha: I think of it this way. Every time a person takes 8 steps, another person takes 5 steps. So 16 steps correspond to 10 steps, and 24 steps correspond to 15 steps. As 20 is halfway bwtween 10 and 15. I got 12 1/2 for the answer. Explain your reasoning.
I will be happy to critique your thinking.