
Why 3×5 is and isn't 5×3 - brainsmith
http://underscore.io/blog/posts/2015/11/17/why-3x5-is-and-isnt-5x3.html
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merb
this is so childish from the teacher.

5x3 == 3x5

Complexity is a major aspect in computing but not in school for
undergraduates.

Also the kid should get a +1 since he used a law of math to reduce the
complexity of the operation. That's more insane than proving this kid wrong.

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FroshKiller
You are confusing the equivalence of the result of the operations with the
equivalence of the operations. The operations are not equivalent. That is the
point. The question is not testing just whether you arrive at the correct
result but whether you arrive at the correct result via the correct operation.
The question clearly prompted the student to apply a particular strategy, and
the student did not correctly apply that strategy. It's very cut and dry.

There is also a big difference between teaching a complex subject to a student
and laying the groundwork for a later class. You can see that in the array
problem on the same test. That's introducing matrices without getting into
full pre-calculus yet.

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astr0n0m3r
The student very clearly applied the repeated addition strategy to solve it.
It's very cut and dry.

