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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!
75% = 3/4
(3/4) * 4 = 3
639% of 1282.5
0.75*4
Why did no one ever teach me this?? Did I miss this day in class? I feel so silly. This is really useful.
Yes and no, other day I was trying to figure out 17% of a number like 65, and I’m like “Oh it’s just 65% of 17!” Which really wasn’t helpful.
It works with small numbers on one side tho.
4*75/100Formulated like this it’s really obvious why the method up there works too
This is the way
Asian Superman knows this
Ah, joy of commutative algebra.
Wait until you get to noncommutative algebra… shudders. No one who mastered that monster of a subject is sane in any measure.
Yay for quaternions and beyond
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.
Mine brain just does 0.75 × 4.
Thought process was…
- Get 1% = 0.75
- Double it = 1.5
- Double it = 3
That’s why you can always double the maximum limits engineers give.
60 mph roadway?
I can do 120 on it no problem.
Eight person elevator? Sixteen.
0.08 BAC? 0.16 easy peasy.
Can I also smoke two joints before I smoke two joints, and then smoke two more?
At that point you will have smoked 4% of 100 joints. Hey, math is easy.
How do Europeans even measure weed lol
In grams bro.
That’s trippy man, so do we.
Yes, in elevators usually one cable could hold far more than the full weight, then they add 5 more for the safety.
For rail speed limits this is the exact way they calculate it. For road speed limits they consider braking distance, which grows by the square of your speed, so if you go 120 on 60 road, you will need 4 times the distance to stop. I wrote 1.5 as a safety factor, not 4, With a 1.5 safety factor you can go by 75 though, but I would use a 1.1 safety there, as in my country the speed cameras are set up that way, you can go +10% of the official speed limit, they only send a cheque if you went even quicker than that.
That’s because elevators use counter weights usually equal to the weight of the car and half the occupancy load so that it takes less energy to lift it and if it falls for any reason it won’t hit the bottom as long as the counter weights are still attached. The occupancy load is determined by the counter weighting system not the cable load capacity.
Yeah, as I understand it, the elevator will refuse to move instead of collapse, and hopefully you’re not between floors when it happens because it was close and someone shifted their weight or bounced slightly or they might write a sitcom episode about what happens next (and the reality will be far more boring).
They send you a cheque for speeding? Sounds like you should be going at least 1.11x to collect your bonuses 😜
(the word you were meaning to use was “fine” or “ticket”)
Did engineers come up with that last one though?
I’m confused by this statement, the answer is 3. Why do all these extra steps for a wrong answer?
It’s not wrong, it’s close enough. And the point it works with more numbers and more type of calculation. Let’s calculate 4% of 1243. That’s the same as 1243% of 4, right, much easier to calculate by simply changing the 2 numbers… While my method is the same, by simply rounding everything.
And in engineering you always multiply/divide your results by a 1.5 or 1.25 safety factor, depending on situation. So you don’t have to calculate exact results, just close enough. E.g. G is always 10m/s2. π is only 3.14, the other digits doesn’t matter.
That’s the stupidest shit I have heard today. You should feel ashamed if you really are an engineer
That’s how engineering is. In civil you can round π=5 for a lot of calculations. In astrophysics I’ve seen e=π=10
Rounding once may be okay but rounding multiple times and that errors add up. Astrophysics?! If im working with wood, i don’t care measuring to 0.1 mm and it might be okay in astrophysics to use 10 for pi, but that doesn’t make guessing your math correct in general.
Maybe we are doing things differently here in germany.
That’s exactly why we have safety coefficients.
Safety coefficients are for nerds
I’d do 4%=1/25, 75/25=3.
Answer
One…
A-two
A-three. Three licks to the Tootsie Roll center of a Tootsie Pop.
You bit that, you cheated! I saw you.
Mr. Owl would be proud
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 * 0.75That’s fair. I intended them to just be a list of equalities
That’s a neat trick but also 4% of 75 = (1% of 75) * 4 = 0.75 * 4 = 1.5 * 2 = 3
Even the first one, 0.75 doubled and then doubled again is hard?
Ya
at this point in my life, as somebody with multiple math degrees, if i ever come across a situation where i need to multiply or divide numbers and one of them is bigger than 12, im going to use a calculator.
Shitty Math Pro Tip: If you ever have to work with numbers larger than 10, convert it to scientific notation and then round to a single significant figure.
? = 0.04 x 75 ? = (4 x 10^-2) x (7.5 x 10^1) ? ~= (4 x 10^-2) x (8 x 10^1) ? = 4 x 8 x 10^-1 ? = 32 x 10^-1 ? = 3.2 ? ~= 3See how easy that is? Here’s another one:
? = 12 x 12 ? = (1.2 x 10^1) x (1.2 x 10^1) ? ~= (1 x 10^1) x (1 x 10^1) ? = 1 x 10^2 ? = 100Bam, lock it in.
Look at Mr big brain over here who learned his times tables. Sure hope nobody takes his lunch money.
Is it weird that I just went
start: 75
to actual decimal: .75
*2*2: 1.5 -> 3
Nah we all do weird shit. I did 4x75, then moved from 300. to 3
Meanwhile im the idiot thats like “uh 10% of 75 is 7.5, half it for 5% of 75 is 3.75, 1% of 75 is .75, so its probably 3?”
Lets pray thats one of the options on the multiple choice. Oh the professor wants me to show my math? Well lets hope he’s open to me being an abstract dumbass that is capable of getting the right answer.
If the professor is actually a professor and not a teacher, they probably appreciate your line of thinking
Yes, but then I have to do 4 x 75 = 50 + 25 + 50 + 25 + 50 + 25 + 50 + 25 = 50 + 50 + 50 + 50 + 25 + 25 + 25 + 25 = 200 + 100 = 300 in that same order because non-maths brain.
I just figured 4% is 1/25 and divided 75/25
That’s how my brain works as well.
