When you need to multiply 7*8 do you simply have it memorized, or do you need to add, subtract or otherwise connect it to another math fact that you know better?
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* because 7 is greater than 5 most of the time when you add it to a two digit number you must carry which is another opportunity to make an error.
* it is not a multiple of 2 so you can't use counting by twos to help
* 9 is easy and there are may tricks to remember the multiples of 9s
* Therefore 7 is the most troublesome number.
@jitterted@sfba.social @futurebird@sauropods.win
7x8 no problem
8x7 takes longer7x7 is always 49 so just add 7
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When you need to multiply 7*8 do you simply have it memorized, or do you need to add, subtract or otherwise connect it to another math fact that you know better?
That is do you simply think "56" or are there more thoughts that lead to 56?
@futurebird 7 * 8 ? This is how I do it i my head
0111
1000
______ apply logical AND of each bit in multiplier to the multiplicand and shift results to match bit position in the multiplier.---0000
--0000.
-0000..
0111... (add all these 4)
_________
0111000 = 8 + 16 + 32 =56 !7 * 5 :
0111
0101
------
...0111
..0000.
.0111..
000...
---------
010011 = 32 + 2 + 1 = 35 !(your question prompted search I had been meaning to do for long on how CPU multiply).
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When you need to multiply 7*8 do you simply have it memorized, or do you need to add, subtract or otherwise connect it to another math fact that you know better?
That is do you simply think "56" or are there more thoughts that lead to 56?
@futurebird At grade school we had to memorize multiplcation table up to 12. I assume kids these days just press the button and ask Siri
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When you need to multiply 7*8 do you simply have it memorized, or do you need to add, subtract or otherwise connect it to another math fact that you know better?
That is do you simply think "56" or are there more thoughts that lead to 56?
@futurebird Computer science is largely just a sillier version of math in general, so I've memorized single digit addition and multiplication, as well as powers of 2 which are important to computers.
I have to manually carry for anything beyond a single digit, which slows me down. -
@futurebird Computer science is largely just a sillier version of math in general, so I've memorized single digit addition and multiplication, as well as powers of 2 which are important to computers.
I have to manually carry for anything beyond a single digit, which slows me down.@futurebird My ex had this thing where, inspired by her father's love of dominoes, would see the numbers as domino pips, and she would quickly smash them together and they'd rearrange and she'd have the answer in half the time it would take me.
It wouldn't work on more complex operations like square roots though. -
* because 7 is greater than 5 most of the time when you add it to a two digit number you must carry which is another opportunity to make an error.
* it is not a multiple of 2 so you can't use counting by twos to help
* 9 is easy and there are may tricks to remember the multiples of 9s
* Therefore 7 is the most troublesome number.
@futurebird @jitterted also: no useful mnemonics for divisibility by 7
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When you need to multiply 7*8 do you simply have it memorized, or do you need to add, subtract or otherwise connect it to another math fact that you know better?
That is do you simply think "56" or are there more thoughts that lead to 56?
@futurebird I have the multiplication table memorized.
It's the addition table I never got down.
I think I was 50 before I finally trusted myself enough to add some numbers without counting up. Like, "3 has three points, count them, 1, 2, 3." -
* because 7 is greater than 5 most of the time when you add it to a two digit number you must carry which is another opportunity to make an error.
* it is not a multiple of 2 so you can't use counting by twos to help
* 9 is easy and there are may tricks to remember the multiples of 9s
* Therefore 7 is the most troublesome number.
@futurebird @jitterted And 7 has no easy pattern to learn. The easiest way to may be to flip it with the commutative property. You may not have 7 x 8 memorized, but you do know 8 x 7.
7 x 6 = 6 x 7
7 x 8 = 8 x 7
etc. -
When you need to multiply 7*8 do you simply have it memorized, or do you need to add, subtract or otherwise connect it to another math fact that you know better?
That is do you simply think "56" or are there more thoughts that lead to 56?
@futurebird when I was young, my eldest sister helped me drill on the tables. It was also the time Multiplication Rock came out on ABC, so I got that wired into my tiny mammal brain.
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When you need to multiply 7*8 do you simply have it memorized, or do you need to add, subtract or otherwise connect it to another math fact that you know better?
That is do you simply think "56" or are there more thoughts that lead to 56?
@futurebird With this and nearly anything else that needs to be calculated, I use a calculator app. I eschew all math.
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When you need to multiply 7*8 do you simply have it memorized, or do you need to add, subtract or otherwise connect it to another math fact that you know better?
That is do you simply think "56" or are there more thoughts that lead to 56?
@futurebird was supposed to memorize the table in school but I didn't so I have to do the math, I'm terrible with memorizing things
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@futurebird when I was young, my eldest sister helped me drill on the tables. It was also the time Multiplication Rock came out on ABC, so I got that wired into my tiny mammal brain.
So, the better question is which song do you use?
( I'm kidding, of course, I already know the answer )
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* because 7 is greater than 5 most of the time when you add it to a two digit number you must carry which is another opportunity to make an error.
* it is not a multiple of 2 so you can't use counting by twos to help
* 9 is easy and there are may tricks to remember the multiples of 9s
* Therefore 7 is the most troublesome number.
@futurebird @jitterted Seems like just recently the most troublesome number is 4.
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@futurebird @jitterted Seems like just recently the most troublesome number is 4.
In some numerologies 4 is considered feminine while 5 is masculine. So, I always get a little salty when people hate on 4 because it seems vaguely sexist.
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When you need to multiply 7*8 do you simply have it memorized, or do you need to add, subtract or otherwise connect it to another math fact that you know better?
That is do you simply think "56" or are there more thoughts that lead to 56?
@futurebird I have dyscalculia and anything larger than 6x6 I can't do in my head so 7x6 could be 56, I dunno
(aside to my middle school math teacher: I carry a calculator everywhere these days, now who's having the last laugh?!)
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When you need to multiply 7*8 do you simply have it memorized, or do you need to add, subtract or otherwise connect it to another math fact that you know better?
That is do you simply think "56" or are there more thoughts that lead to 56?
@futurebird I simply do not multiply 7*8
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In some numerologies 4 is considered feminine while 5 is masculine. So, I always get a little salty when people hate on 4 because it seems vaguely sexist.
@futurebird @jitterted I was thinking specifically of this: https://www.theregister.com/security/2026/10/20/indian-certification-authority-emudhras-private-keys-compromised-one-of-them-was-the-number-4/5304312 It's become a bit of a meme lately.
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@futurebird Computer science is largely just a sillier version of math in general, so I've memorized single digit addition and multiplication, as well as powers of 2 which are important to computers.
I have to manually carry for anything beyond a single digit, which slows me down.I always imagined she was over-serious the silly child of mathematics is Pure Math
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@futurebird @jitterted And 7 has no easy pattern to learn. The easiest way to may be to flip it with the commutative property. You may not have 7 x 8 memorized, but you do know 8 x 7.
7 x 6 = 6 x 7
7 x 8 = 8 x 7
etc.@futurebird @jitterted 7 x 7 is a hopeless case. Hopefully, it never comes up.
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When you need to multiply 7*8 do you simply have it memorized, or do you need to add, subtract or otherwise connect it to another math fact that you know better?
That is do you simply think "56" or are there more thoughts that lead to 56?
@futurebird For me it's connected to my "most remembered" part of multiplication table -> 7*7. Then I just add one more 7 to the result.
It's not that much slower than having it remembered, so I never bothered to "optimize" it.
