• Jo Miran@lemmy.ml
        5·
        10 months ago

        I see them as the same except that your way illustrates what his parentheses are doing.

        • Cheradenine@sh.itjust.worksEnglish
          1·
          10 months ago

          The way I see it the parentheses are good, it the 17x3 that hurts my brain.

          It’s already broken down, then gets more complicated by the 17x3. In my mind I now need to separate 17 into 10 and 7 then multiply them each by 3 and add them together, which is where we started in the first place.

          Brains are different, that’s how mine goes though.

          • Jo Miran@lemmy.ml
            1·
            10 months ago

            I understood that to be a reference to the original screenshot. Thus the two equal signs. It was a way to walk you through how the breakdown ties back in.
            ¯\_(ツ)_/¯

            • Cheradenine@sh.itjust.worksEnglish
              2·
              10 months ago

              Not disagreeing, and I upvoted you for a different perspective. I did not see it that way, though I do now.

              Like I said, brains are different.

    • sugar_in_your_tea@sh.itjust.works
      1·
      10 months ago

      Or the way I do it:

      • 3 * 20 = 60
      • 60 - 51 = 9
      • 20 - (9 / 3) = 17

      So the factors are 17 and 3. I know 3 is a factor because 5+1=6, which is divisible by 3, so I just use a convenient multiple of 3 that’s pretty close to the actual number to get the divisor.

      I have young kids and they keep asking me to do crazy math problems while driving, so that’s generally the trick I use.

    • Jo Miran@lemmy.ml
      1·
      10 months ago

      This is how I have always calculated in my head. It used to drive my mom and my teachers crazy when they asked me to verbalize my calculations. It was like I was hurting them somehow. I never understood why.

  • yarr@feddit.nlBanned from communityEnglish
    10·
    10 months ago

    If it makes you feel any better, it’s just (20 x 3) - (3 x 3).

    I don’t know why, but that makes me feel better.

    • JasonDJ@lemmy.zip
      9·
      10 months ago

      This must be the new math that parents are so scared of.

      Back in my day, we multiplied 3 by 17 because that’s how you do it. You multiply 3 times 7, you multiply 3 times 10, and you add. Simple.

      Adding three to 17, to make it 20, multiplying that by 3, and then multiplying that 3 by 3 to subtract js equally valid, and easier to work out mentally IMO. It lays the framework for good estimation skills, too.

      • PM_Your_Nudes_Please@lemmy.world
        10·
        10 months ago

        and easier to work out mentally IMO.

        And this is the key factor to why math teaching has changed. Rote memorization is actually really really awful for learning.

        Teaching math used to be a case of having students fill out their times tables. I still remember having to fill out this chart in under 5 minutes:

        This was a quiz that we had to do multiple times per week. It was given to us blank, and 5 minutes obviously isn’t enough time to actually calculate everything; We were expected to have it memorized. And when the students had memorized the table, the quizzes changed into a series of small calculations from the table, again under 5 minutes. So if we ever had to calculate anything out, we could just refer to our memorized times table and pull the number off of that. But the issue is that this only works up to a certain point; Nobody is going to be able to reasonably memorize their times table beyond maybe 15x15. And this means that the times table essentially becomes worthless for doing math in larger numbers.

        So instead, the “new” math teaches students how to take complicated problems (like 17x3) and break it down into easier steps. 17x3 is complicated, but 20x3 is just 2x3 with an added 0, and 3x3 is easy too. So if we can convert 17x3 into (20x3)-(3x3) then it becomes much easier to do in your head. Because not everyone can calculate 17x3 accurately, but virtually anyone beyond 1st grade can calculate 60-9.

        The “new” math was developed by studying how the students who were good at math actually did their calculations. And it turns out, when you actually understand the concepts, you can create mental shortcuts to break the difficult problem down into a series of smaller problems. And that’s exactly what the “new” math does.