How well do you know the multiplication table?

[Tosh5457]

I knew it in the first years of school, nowadays I just calculate them. It's easy if you make it into parts, 7*3 + 7*3 and it's easy.

 

[Charles Kottler]

If you're going to be doing arithmetic often it is worth learning tables to save time. At school I was taught by wrote - two twos are four, three twos are six etc. up to 12x12. These stuck with me and when I was about 30, while training for a half marathon I extended this up to 20x20 - not much else to do while bashing out the miles at night :).

 

[Kevin McHugh]

When I was 4th grade, my father drove me to school. He made me recite my 12 x 12s every morning. I also had to memorize perfect squares up to 20.

 

[virus205]

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Regards

 

[WWGD]

When I was 4th grade, my father drove me to school. He made me recite my 12 x 12s every morning. I also had to memorize perfect squares up to 20.

I knew my 1x1s table by 3! :).

 

[Mark44]

I knew my 1x1s table by 3! :).

That's quite old! 3! = 6, and 3! = 6! = 720. I don't really believe you're that old.
It shouldn't take more than a year or two to learn all the products in that table...

 

[micromass]

That's quite old! 3! = 6, and 3! = 6! = 720. I don't really believe you're that old.
It shouldn't take more than a year or two to learn all the products in that table...

Actually, the double factorial is defined differently than that https://en.wikipedia.org/wiki/Double_factorial
So $3! = 3$, which is in line with his statement.

However, I think this notation for double factorials is pretty horrible.

 

[Mark44]

You're right, micromass. I was interpreting 3! as (3!)!

 

[DaveC426913]

I did this in my head while (failing) to fall asleep. Can't bring a calculator to bed.
https://www.physicsforums.com/threads/joystick-geometry.885203/#post-5568515
I did it rounded to zero decimal places in my head, then followed up in the morning with pencil and paper to one decmial place.
I could do it to an arbitrary number of decimal places*, but there's no point.

*OK, I can't do square roots to more than one decimal place.

 

[WWGD]

You're right, micromass. I was interpreting 3! as (3!)!

But the smiley takes care of any doubt :) (