• andros_rex@lemmy.world
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    5 hours ago

    The vast majority of people do not understand fractions. Even math teachers do not understand fractions. I quiver in horror every time a student says the words “cross multiply” because I am about to see some gruesome debasement of mathematics.

    • Zink@programming.dev
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      2 hours ago

      I had to remind myself exactly what the point of cross multiplying is.

      …it’s essentially just a label given to a specific set of algebraic operations. That it even has a name seems stupid to me. We shouldn’t focus on memorizing specific cases like this when understanding why it works will get you there just as quickly. Heck in the case of cross multiplying, I think it works against the interests of the students’ learning. It’s a shortcut that hides the fact that you’re multiplying both sides by both denominators, when “do the same thing on both sides of the equals sign” is algebra 101.

      • andros_rex@lemmy.world
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        2 hours ago

        Exactly. The problem is that they will also start “cross multiplying” any time they see a fraction. “Okay, so what do I need to do if I want to add 3/4 + 1/3?” And then they’ll say “cross multiply”?

        Just say - “hey, the way to get rid of the denominators is to multiply everything by the LCD.” Then it works in all cases. No weird “one trick” that doesn’t really teach them anything.

        (But, where I live - the people teaching math don’t understand math lol.)