Pocket cube!

Without disassembling the cube, how many possible combinations are there in a 2 × 2 × 2 2 \times2 \times2 Rubik's cube?

Hint:

  • 2 × 2 × 2 2\times2\times2 Rubik's cube has no fixed center.

  • There are 8 8 corners.

  • I don't think you will find answers somewhere. Calculators allowed.


The answer is 3674160.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

The eight corners positions: 8 ! \displaystyle 8!

But seven of them can be independently rotated 3 7 \displaystyle 3^7

There is nothing identifying the orientation of the cube in space. This is because all possible positions of the corners are equivalent and no center like 3 × 3 × 3 3\times3\times3 . We can do that by canceling × 8 \times 8 in 8 ! 8! and ÷ 3 \div3 in 3 7 3^7

The possible combinations are: 7 ! × 3 6 = 3674160 7!\times 3^6= \boxed{3674160}

Luke Cai
Aug 23, 2015

(I had to use paper and calculator to solve this)

With eight corner positions, there are a total of 8! possible ways to arrange them, as n number of items can be arranged without repeating itself n! times.

If one of these corners remains in the same place, that leaves seven other corners that can be rotated independently, meaning there are 3^7 or 2187 combinations.

Due to the fixed center (thanks for the hint), there is no initial orientation like a regular Rubik's cube, rotated by any means, resulting in 3 * 8 times less positions .

This reduces down to 7! * 3^6 solutions, or 3674160 ways.

Fun Fact: I could never solve one of these (I'm not the brightest person), so I made one out of 8 6 sided dice and magnets so that you could take apart and solve it if you got frustrated. So worth the time.

I usually solve this cube in under 20 moves. :D

Adam Phúc Nguyễn - 5 years, 9 months ago

Log in to reply

It kind of frustrates me when people solve these things so fast. I commend you for your intellect. For Pete's sake, I could never solve a regular 3x3x3 Rubik's cube without having someone help me or using an answer sheet- even that takes me over 20 minutes >:(

Luke Cai - 5 years, 9 months ago

Log in to reply

Oh, my record for 3x3x3 is 9.57 seconds :D By the CFOP method. It's easy. I can also solve 4x4x4 cube to 6x6x6 cube. it's nno difference from the original, just more peices;

Adam Phúc Nguyễn - 5 years, 9 months ago

Log in to reply

@Adam Phúc Nguyễn Ahh, yes, the CFOP method that has blessed many speed cubers and cursed me because I stumble with pattern recognition. Sometimes I get too excited and try to solve a face or make a line, only to ruin the rest of the pattern (patience is certainly a virtue) . I do realize that the bigger cubes follow the same format, but they just take longer. Mind you, I can solve a 1x1x1 cube in 0 seconds. A lot of people can match it, but I don't think you can beat that.

Luke Cai - 5 years, 9 months ago

Log in to reply

@Luke Cai I hold the 1x1x1 cube, smashed the timer. I broke the speed of light.

Adam Phúc Nguyễn - 5 years, 9 months ago

Log in to reply

@Adam Phúc Nguyễn Well it takes time to to smash the timer- I don't think you're The Flash from DC comics (or are you?) If you did, you just destroyed nearly everything Einstein theorized. Congratulations. You broke physics. Tell the Nobel Institute of your accomplishments.

Luke Cai - 5 years, 9 months ago

@Adam Phúc Nguyễn Whoa !! You're so fast !! Mine is 52 52 seconds(seems like a turtle in front of you).

Akshat Sharda - 5 years, 7 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...