## Oct 31 = Dec 25

How can Oct 31 and Dec 25 be the same?

Because Oct 31 represents the octal (base 8) number 31, which, when converted to decimal, is 25. Dec 25 is short for Decimal 25, thus the two are equal.

Posted in Brain Teasers

13 Comments on "Oct 31 = Dec 25"

fivebee says
February 7, 2014 @ 22:59

because they’re both fall/winter holidays. 10/31 is halloween and 12/25 is christmas

Jasmine says
November 8, 2014 @ 12:54

Still don’t get it

Surf Diva says
January 25, 2015 @ 23:05

Ahhhh – a great nerdy math/programmer joke. The answer is that what appears as dates is really referring to numerical systems. Oct = octal, which is a base 8 numbering system and Dec = decimal, which is base 10.

It looks like this:

Octal numeration: 0, 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13 ,14, 15, 16, 17, 20, 21, 22, 23, 24,25, 26, 27, 30, 31

Decimal numeration: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25

Emma says
May 3, 2015 @ 23:33

Oct 31my 3 quarter birthday and dec25 my eleven twelfth birthday

Lily says
May 4, 2015 @ 21:55

I agree with surf diva for Oct 31 = Dec 25
I also think that Oct 31 = Dec 25 because October 31 is A holiday, Halloween and December 25 is also a holiday, Christmas

Allen says
May 11, 2015 @ 15:23

Awesome riddle!

Christine says
February 2, 2016 @ 09:43

Q: Why do programmers always get Christmas and Halloween mixed up?
A: Because DEC 25 = OCT 31
It’s a common nerdy math/programmer joke.
Octal = 31
Decimal= 3×8¹+1×8⁰ = 25

Bart says
January 15, 2017 @ 19:48

october is the 10th month, december the 12th
31 (mod 10)=1
25 (mod 8)=1
31 october=25 december

elle says
January 26, 2017 @ 23:57

i think that this is a good joke. 2 years ago my 2 friends lily and emma commented.

Superwhiz Maths Person (also neutral as to not offend those who have a complex of themselves and others) says
March 10, 2018 @ 20:50

Funny thing is, both dates are the same too. It is like this:
1) alarm rings
2) wake up, brush teeth
3) stare at computer screen for hours on end
4) toilet break, food, etc
5) stare at computer screen for a few more hours
6) shower
7) bed.
* some intimate details have been left out not to make it too boring or long.

Pizza Bubble says
April 8, 2020 @ 07:33

Surf Diva is 100% right. That’s the only reason.

Howard says
July 24, 2022 @ 18:43

31 oct base= 25 dec base

Tom says
February 2, 2024 @ 19:28

It’s the same number in different number systems. Computers use base 2, 8, 16. We use base 10 since we have 10 fingers. So in the octal (base 8) number system 31 means 3 x 8^1 + 1×8^0 which is 25 in the base 10 (DEC). Life would be easier if we have fingers that were powers of 2.