Current Events > 12! + 10! = 4a26b04c0

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FLOUR
08/25/23 5:40:02 PM
#1:


Supposed you need to find the unknown digits but didn't want to compute this disgusting number by hand. How would you go about finding the digits? What are they? This would be an ideal number theory test question.

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Serious_Cat
08/25/23 5:59:54 PM
#2:


I feel like I'm missing something here. 12! would include another 10 and both have a 5 and 2 to multiply so the third digit from the left would be another 0 rather than 4.

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R1masher
08/25/23 6:01:08 PM
#3:


Same way you did, ask somebody

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Trumble
08/25/23 6:01:39 PM
#4:


Serious_Cat posted...
I feel like I'm missing something here. 12! would include another 10 and both have a 5 and 2 to multiply so the third digit from the left would be another 0 rather than 4.
Given that the answer is in hex, I'd assume 12 and 10 are too.

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Homeless_Waifu
08/25/23 6:01:40 PM
#5:


How does one even get letters?
Sorry for my ignorance, i get lost when it comes to math

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Serious_Cat
08/25/23 6:03:22 PM
#6:


Ah. I thought the letters were the unknowns.

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AngelsNAirwav3s
08/25/23 6:03:49 PM
#7:


Trumble posted...
Given that the answer is in hex, I'd assume 12 and 10 are too. (ie. They represent the decimal values 18 and 16)

I think the numbers are base 10, and TC just wrote the unknown digits as a/b/c instead of the normal x/y/z

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Tyranthraxus
08/25/23 6:06:52 PM
#8:


Serious_Cat posted...
I feel like I'm missing something here. 12! would include another 10 and both have a 5 and 2 to multiply so the third digit from the left would be another 0 rather than 4.

10*5*2 is 100 so that means c is zero, not the third digit.

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Giacomo_Hawkins
08/25/23 6:10:52 PM
#9:


Serious_Cat posted...
I feel like I'm missing something here. 12! would include another 10 and both have a 5 and 2 to multiply so the third digit from the left would be another 0 rather than 4.

You're on the right track, but not quite.

The 5 and 2 mean that all factorials 5! or higher end in a zero. The 10 adds a second zero digit. 15 would add a third. 20 adds a fourth. Ect.

Adding two factorials 10! or higher does not mean that the third digit would become zero, but you can safely conclude that the 'c' is zero.

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Giacomo_Hawkins
08/25/23 6:20:36 PM
#10:


Also, echoes of this topic.

https://gamefaqs.gamespot.com/boards/400-current-events/80544903

I'm sensing a theme here.

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Justin2Krelian
08/25/23 6:24:44 PM
#11:


Reminds me of when someone used a number that was something like 111!!!!!!!!!! in a "biggest numbers" contest.

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Giacomo_Hawkins
08/25/23 7:45:16 PM
#12:


Justin2Krelian posted...
Reminds me of when someone used a number that was something like 111!!!!!!!!!! in a "biggest numbers" contest.

Not as large a number as they may have intended:

https://mathworld.wolfram.com/Multifactorial.html

Every additional exclamation point makes the result smaller.

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BewmHedshot
08/25/23 7:55:18 PM
#13:


Are we like pretending we don't have a calculator? 482 million isn't remotely a computationally intractable number where you need modular arithmetic.
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Anteaterking
08/25/23 8:05:49 PM
#14:


You can use modular arithmetic for problems of this sort (reducing things modulo 100 will give you the bottom two digits and you only need to track those two values throughout which makes it easier to do things by hand).

e.g. I can tell you that 3^(5000000) ends 01 because 3^20 = 1 mod 100.

This method doesn't really help that much with factorials though because the digits are all slowly annihilated by the 5s and finding digits closer to the front would be basically the same amount of memory and work as just calculating the factorial.

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Justin2Krelian
08/25/23 8:58:45 PM
#15:


Giacomo_Hawkins posted...
Not as large a number as they may have intended:

https://mathworld.wolfram.com/Multifactorial.html

Every additional exclamation point makes the result smaller.

Interesting, though they must have intended the factorial of the factorial of the factorial... and so on. These were smart mathematicians so there must be some detail I'm missing.

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thisworld
08/25/23 9:23:34 PM
#16:


So basically I have to find out a, b, and c? Fine, let's do this by hand.

12! + 10! = 4a26b04c0
(12 * 11 * 10!) + 10! = 4a26b04c0
(132 * 10!) + 10! = 4a26b04c0
(132 + 1) * 10! = 4a26b04c0
133 * 10! = 4a26b04c0

c = 0 because the left side of the equation has 10 * 5 * 2 = 100 as factor (comes from 10!). Divide the whole equation by (10 * 5 * 2)

133 * (9 * 8 * 7 * 6 * 4 * 3) = 4a26b04

Find the prime factorization for the left side of the equation

(7 * 19) * (3^2 * 2^3 * 7 * (2*3) * 2^2 * 3) = 4a26b04
2^6 * 3^4 * 7^2 * 19 = 4a26b04

Left side has 2^6 = 64 as a factor. This includes 32, 16, 8, 4, and 2 as factors too obviously. Observe the divisibility rule with 2^x as divisor:
--------------------------------
2 as factor = the last digit is divisable by 2
4 as factor = the last 2 digits are divisable by 4
...
64 as factor = the last 6 digits are divisable by 64
--------------------------------

2^6 * 3^4 * 7^2 * 19 = 4a26b04

4a26b04 has 2^5 = 32 as a factor which means the last 5 digits, 26b04, are divisable by 64. Calculate 26b04/64 by hand with all the possible combination (b = 0, b = 1 ... b = 9). Only one possible value of b makes 26b04 divisable by 64 and that is b = 3

2^6 * 3^4 * 7^2 * 19 = 4a26b04
2^6 * 3^4 * 7^2 * 19 = 4a26304

Left side has 3^4 = 81 as a factor which means 27, 9, and 3 as factors too. Observe the divisibility rule with 9 as divisor:
--------------------------------
Sum the digits. The result must be divisible by 9
--------------------------------
4a26304 has 9 as a factor. 4+a+2+6+3+0+4 = 19+a must be divisable by 9. a = 8

c=0, b=3, a=8

12! + 10! = 4a26b04c0
12! + 10! = 482630400

QED

...wtf did i just do? doing someone's homework on gamefaqs lol
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Anteaterking
08/25/23 9:32:07 PM
#17:


thisworld posted...
So basically I have to find out a, b, c without doing a single multiplication operation?


thisworld posted...
c = 0 because the left side of the equation has 10 * 5 * 2 = 100 as factor


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thisworld
08/25/23 9:55:15 PM
#18:


Anteaterking posted...
thisworld posted...
So basically I have to find out a, b, c without doing a single multiplication operation?


thisworld posted...
c = 0 because the left side of the equation has 10 * 5 * 2 = 100 as factor

lmao hahahaha! okay okay...

Goddammit I had a brain fart there. You're absolutely right though. It is a multiplication operation, no matter how simple.

I erased that 'no multiplication' stuff. Don't tell anyone... lol
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thisworld
08/26/23 12:21:18 AM
#19:


Jesus I just realized that I made a typo up there!

thisworld posted...
4a26b04 has 2^5 = 32 as a factor which means the last 5 digits, 26b04, are divisable by 64. Calculate 26b04/64 by hand with all the possible combination (b = 0, b = 1 ... b = 9). Only one possible value of b makes 26b04 divisable by 64 and that is b = 3

It is 32 NOT 64. It should've been:
4a26b04 has 2^5 = 32 as a factor which means the last 5 digits, 26b04, are divisable by 32. Calculate 26b04/32 by hand with all the possible combination (b = 0, b = 1 ... b = 9). Only one possible value of b makes 26b04 divisable by 32 and that is b = 3

I actually did the proper calculation using 32 as divisor. Bloody hell I have no idea how that '64' managed to slip in there >.<

I'm sorry everyone.
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ChocoboMogALT
08/26/23 12:36:56 AM
#20:


thisworld posted...
I actually did the proper calculation using 32 as divisor. Bloody hell I have no idea how that '64' managed to slip in there >.<

I'm sorry everyone.
That's what you get for throwing in the QED.

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thisworld
08/26/23 12:55:09 AM
#21:


ChocoboMogALT posted...
That's what you get for throwing in the QED.

Haha yeah. Apparently my brain was out of sync with my hand or something during that particular part. Still can't believe I missed that!! Well lesson learned, gamefaqs and math don't mix
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Robot2600
08/26/23 1:29:53 AM
#22:


okay now explain how in the fuck that was easier than computing on scratch paper

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