Once again, frustrated parents are posting their children’s math assignments on social media.

Insane Common Core math problems go viral, reports Tech Insider. In one, a student is marked wrong because he or she got the right answer by subtracting rather than estimating.

In the other assignment, a third grader was asked to use “repetitive addition” to solve 5 x 3. The answer — 5 +5 +5 = 15 — was marked wrong. The teacher wanted 3 +3 +3 +3 +3 = 15.

The student’s array showing 4 x 6 = 24 also was marked wrong. The teacher wanted rows of 6 hashmarks in 4 columns.

Whatever happened to the commutative property?

Estimation and repeated addition, are part of the Common Core standards, said Noschese. However, it’s up to teachers to design lessons and tests.

Don’t assume the teacher is an idiot, writes Hemant Mehta on Patheos.

Thinking of 5 x 3 as, literally, “five groups of three” could help students learn division, he argues.

When they see a problem that says 5 x ___ = 15, they’ll be thinking “I need five groups of SOME NUMBER to get to 15.” In other words, they’ll be able to pick up division a little more quickly because they’re learning the proper way to think now.

The array problem will make sense in algebra class. “There’s a difference between a 2 x 3 matrix and a 3 x 2 matrix.”

I got through advanced algebra and trig without hitting matrixes. Perhaps they hadn’t been invented then.

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