March 26, 2017

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Consider the following students’ methods 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 by 5 and got 12 ½ 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 between 16 and 24, I reasoned
that the answer was halfway between 10 and 15. I got
12 ½ for the answer.
Explain your reasoning.

I feel that both methods were correct in determining the answer, they were both based on comparison, the first one cross multiplied where the second one used equivalent ratios ?
Is that correct ? am I wrong or missing something ?

  • Math, check my answer. thanks - ,

    OK except for your typo. 12 1/2 is correct, not 2 1/2

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