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# Similar Figures What’s the fastest way to help this student?

Thanks to Nico for the submission.

## 4 replies on “Similar Figures”

It sure looks like they are adding the same number to both side lengths. 72 – 16 = 56, and then 56+12 = 68. So I would probably try and do some more examples, probably using grid paper so that they have another way of checking their answer besides the similar triangles algorithm they are using.

First, the student is using additive reasoning instead of multiplicative reasoning. Multiplicative reasoning is usually considered more developmentally advanced so a good question to ask “Is the student developmentally ready?”

An even better question to ask is, “Is multiplicative reasoning needed?” Based on the given information, I do not see anything to indicate that these two shapes are similar, or that the sides are proportional. As such, it would be difficult to predict the poster’s height without more information or making some assumptions.

David:
Working on a grid is offered to students as one possible way to combat the additive reasoning (good suggestion). There are a few others such as scaling it down: is 3 the answer to 1/2 = ?/4 as additive would suggest. Or is 99 the answer to 1/2 = ?/100. But these examples might not work if we address
Chris: