Exactly. Math has historically relied on rote memory for most mental math. Kids would have to fill out their times tables, addition tables, etc until they memorized them. I still remember getting pop quizzes in elementary school that looked like this:

You only had two minutes to fill out the entire thing, which meant you only had 1.2 seconds per answer. You didn’t have time to actually calculate them. The point was that you were expected to have them memorized ahead of time instead of calculating each one.

But rote memory is laughably bad at actually teaching concepts. You may know that 12x5 is 60, but you don’t have any understanding on why, or other ways to do that same calculation without rote memory. And rote memory is only decently reliable up to ~12x12. Anything past that, and it becomes too much info to track; kids simply start forgetting answers.

The kids who were good at math (and I mean actually good at math, not just good at memorizing things) quickly devised methods to do this shit in our heads easily. Keeping track of multiple numbers in your head gets confusing. So “line them all up, add straight down, and carry 1’s” sort of falls apart if you’re doing it in your head. Especially if you’re trying to keep track of more than three or four numbers at a time.

Essentially, 127+248+30 is the same as 105+250+50, but the latter is much easier to parse in your head. But yeah, the parents (who primarily relied on rote memory) didn’t understand why the new method would be more effective, because they didn’t understand the concepts surrounding the math.

I was trying to explain how and why they were teaching math to a family friend and they didn't get it(multiplication stuff). I broke it down with pen and paper and they didn't get it. Simpler example, nope. Eventually I had to explain how multiplication is just repetitive addition. They responded with WHAT! and I realized why they always wore open toed shoes. I sent them a link for 5th graders.

As a parent who is bad at math, you’re not wrong. But given my kids are excelling in math (very high scores), I’ve learned to shut the fuck up about it and let the teachers do their black magic jobs.

Those sorts of breakdowns are exactly what the kids who were good at math were always doing, and teaching methods eventually caught up and realized they should just teach the tricks.

Well... kinda. "Getting to 10" was what New Math was trying to teach. So you'd take the 1 from 7 and give to 9, because 6 + 10 is easier than trying to finagle your way to 8x2.

Then a bunch of parents who were bad at math asked “new math? How can math change?”

You don't have to be bad at math, strictly speaking. But there was a lot of brute memorization in traditional math. Times Tables, for instance, were something you just memorized straight up without thinking too deeply. Getting 16 out of 7+9 was something you just had to do on your fingers until you had it lodged in your head.

Old Math tended to be slower and more tedious. New Math is more logical, but also somewhat counterintuitive until you get into the swing of it.

The fact that they even asked that question showed how their math education was lacking, but they seem to have won.

I've got friends with kids down in Houston. "New Math" appears to be alive and well, in no small part because it helps kids score higher on standardized tests.

As someone who learned not via Common Core, and then found out Common Core taught math how I taught myself to do mental math I was a little envious that kids would learn my “easier” method.

He's a spider monkey with base 8 fingers.

Because making shit equal, be in perfect balance or even symmetric makes my dopamine go 🥳.

Finding the correct answer that way is a neat side effect too.

Multiplying by 5: mult by 10 divide by 2

A very similar concept for tipping about 20% is taking 1/10th of the bill by moving the decimal one to the left and doubling that. To make it even easier for me I just round to the nearest $10 amount first.

Bill: $66.20 -> move left and round up = $7.00 and double to $14.00. The exact 20% amount is a little over $13 but I tend to round up because it is also faster to add whole dollars to the bill.

I only read this thread to make sure someone was right. Thank you

That's how I do it in my head too. Is this even uncommon?

Take 7 from 7 and its 16+0 =16

This is what I go for...Just play in 10s. Alot easier IMO

Just as acceptable