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this post was submitted on 20 Oct 2025
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One…
A-two
A-three. Three licks to the Tootsie Roll center of a Tootsie Pop.
4*75/100
Formulated like this it's really obvious why the method up there works too
No. Stop it. Just multiply them together. This is useless.
I only learned this a few months ago here on Lemmy and still don't believe it. It's magic. You think you're going to "get it" (trick it) this time, but nope! Still works somehow!
What’s funny is that if someone said (a * b) * c is the same as (c * b) * a, you’d probably say “of course it is”.
Same trick here if you show it as (4* 1/100) * 75 rewritten as (75 * 1/100) * 4.
4% is 4 in a hundred
75 is 3/4 of a hundred
4% of 75 is 3
0.04 x 75 == 0.75 x 4 == 75 x 4 x 0.01
switch the order of the last two terms (the second equality), put the 0.01 in the middle, and it makes a bit more sense when read as calculation steps.
0.04 * 75 = 4 * 0.01 * 75 = 4 * 0.75
4% is 1/25. 75 is 3*25. so the answer is 3!
3! = 3*2*1 = 6
That's the same order of magnitude, so still correct!
My engineering brain says it's 3.25.
4% is ~ 5%. 10% of 75 is 7.5. To get the 5% I have to divide it by 2, so 4% of 75 is close to 3.25. I will have to multiply it with some safety coefficient at the end, so the exact value doesn't matter.
Yuck. 75 is such a clean number to work with in percentages, it's 3/4 of a hundred
3/4 of 4 is then easy
I'm confused by this statement, the answer is 3. Why do all these extra steps for a wrong answer?
Yeah, this will be so helpful when I'm trying to figure out 20% of 36.23!
Look, move the decimal one to the left, you've now got 10%. Double that and you've got 20%. How often are y'all trying to find out percentages of nice even numbers like that?
See I love quick and dirty rules to get close enough through estimation for whatever I'm mental mathing, because if I need exact numbers I'm turning to a computation device
20% of 36.23 I'd be going "okay 20% of 10 is 2, 3 10s in 36 so 3x2=6, and 6.23 is pretty close to half 10 and half 2 (from my previous 20% of 10 calculation) is 1 so 20% of 36.23 is slightly more than 7"
36.23% of 20 I'd be going "30% of 10 is 3, 2 10s in 20 so 2x3=6, 6.23% is close to 5 so half of 3 is 1.5, 6+1.5=7.5 so 36.23% of 20 is a bit more than 7.5"
Now which is closer to correct? Ehh I'm not sure I haven't used a calculator yet, but I'm mental mathing so chances are my estimation got me close enough that I can just round to whichever direction is safer for errors and call it good. Usually I'm mental mathing to figure out splitting a bill, a tip or to double check some machine computed math that looks wrong, and none of those call for perfect precision, just getting close enough that it doesn't matter
Why did no one ever teach me this?? Did I miss this day in class? I feel so silly. This is really useful.
Most teachers will write it off as obvious. Taking a percentage of something is just multiplication and if you actually write it down with multiplication, it is, indeed, obvious:
4*75/100=75*4/100
And yes, it means you can just multiply 75 by 4 first and then divide by 100.