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Comment by opportune | Hacker News Reader

I do mental math all the time. Nobody needs to memorize tons of math but it's laughable that you would take that to such an extreme that you can't do basic multiplication without a calculator.

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Can you give the example of the last mental math calculation you did? I almost never do it and I still almost never did it even when I was in college taking higher math. Tip calculation is all I can think of.

I work in big data/cloud stuff so I do estimates all the time to figure out what size resources I need/how long something will take. Less than 5 minutes ago I did mental math to see how long a job would take (I knew how long it would take for one read, and I had 2 days of reads over 3 data sources each with 8 data partitions => 48 reads each taking about 90 seconds => about 1.25 hours).

Tip is another thing. And I like to "min/max" grocery shopping so I typically do mental math when shopping to maximize things like grams of protein/$.

I do rough division all the time in my head, for instance figuring out how much each can of beer costs if a slab of 24 is $60. Or on the flip side, how much it's going to cost me to get a round of 4 beers at $8 each.

It's just a general life skill.

I can be claustrophobic..I don’t like being in a closed car..so when I am at traffic stops..I convert alphabets to numbers and numbers to alphabets of the license plates..and sometimes I add the numbers together to check if it’s a prime number. Calms me the fuck down.

in farming..construction..cooking..I use it all the time in my everyday life.

I may chime in with another story. I‘m teaching operating systems at university and use these skills (for small numbers, and written multiplication/division for slightly larger ones) all the time. My general consensus after overseeing a few hundred students is that those that are unable to quickly do simple math in their head also struggle with the rest of the curriculum. Especially if they need a calculator for computing 57:2 everybody gets distracted and we have like 2 minutes idle time while everybody starts entering the equation. I’d rather spend my time teaching actual os stuff, it’s a shame enough that I have to teach how to decimal <-> binary <-> hexadecimal base conversion.

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