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#16

mrparkinglot (07/04/2013) [+] (15 replies)
or you could... I don't know..... USE A CALCULATOR?
I mean... they are everywhere now, on your phone, your computer on your.. yeah calculator
I mean... they are everywhere now, on your phone, your computer on your.. yeah calculator
#31

anonymous (07/04/2013) [+] (3 replies)
I don't like math 'tricks' unless I know why they work.
#6

hounding (07/04/2013) [+] (7 replies)
useless for anything less than 80*80ish because you would end up multiplying double digits anyway
ex: 78*75
22+25=
22*25=
why have i wasted 15 minutes of my life on this ._.
ex: 78*75
22+25=
22*25=
why have i wasted 15 minutes of my life on this ._.
#18

thumbsupforyou (07/04/2013) [+] (3 replies)
The method I use for numbers lower or higher than that is also pretty easy, even if it looks a bit complicated before you try it yourself:
Let's try 147*221:
210

147
221
The last digit of every number matches the 0, the second one from the right matches the 1, and so on, increasing by 1 the further you go to the left
Now you multiply all numbers possible with a summed up indicator of 0 (in this case it's only the last digits of both numbers as only 0+0=0) and add the results. In this case it's just 7*1=7 which is the last digit of the result. Now you do the same thing for every number up to 4 (as the highest digit of both numbers has an indicator of 2 and 2+2=4):
xxxx7 (result until now)
next digit: 4*1+7*2=18 (indicators 1+0=1 and 0+1=1)
write down the 8, remember the 1:
xxx87, +1 remembered
next digit: 1+1*1+4*2+7*2=24 (remainder of the last result, 2+0=2, 1+1=2, 0+2=2)
xx487, +2 remembered
next one: 2+1*2+4*2=12 (remainder, 2+1=3, 1+2=3)
x2487, +1 remembered
last one: 1+1*2=3 (remainder, 2+2=4)
Result: 32487
Sorry for my bad english, this made it look far more complicated than it had to be
Let's try 147*221:
210

147
221
The last digit of every number matches the 0, the second one from the right matches the 1, and so on, increasing by 1 the further you go to the left
Now you multiply all numbers possible with a summed up indicator of 0 (in this case it's only the last digits of both numbers as only 0+0=0) and add the results. In this case it's just 7*1=7 which is the last digit of the result. Now you do the same thing for every number up to 4 (as the highest digit of both numbers has an indicator of 2 and 2+2=4):
xxxx7 (result until now)
next digit: 4*1+7*2=18 (indicators 1+0=1 and 0+1=1)
write down the 8, remember the 1:
xxx87, +1 remembered
next digit: 1+1*1+4*2+7*2=24 (remainder of the last result, 2+0=2, 1+1=2, 0+2=2)
xx487, +2 remembered
next one: 2+1*2+4*2=12 (remainder, 2+1=3, 1+2=3)
x2487, +1 remembered
last one: 1+1*2=3 (remainder, 2+2=4)
Result: 32487
Sorry for my bad english, this made it look far more complicated than it had to be
#71

sweetellie (07/04/2013) [+] (19 replies)
Everyone's discussing maths and I'm just sat here being excited that Bernard Black/Dylan Moran is on the front page.