MathCrazy: 9,999 Reasons Why .999 is One (amazing video)

If you’re a math geek, you’ll love this. Hang onto your hat — and let this math whiz try to convince you — with 9,999 reasons — that that .999 repeating numeral is really one.

She makes a great argument. Do you agree?

Check in with comments below. Thanks to Vihart for this incredible, fast-paced and, our EIC Gina thinks, is an altogether convincing argument. She is running this by me — and her math whiz co-author Steve Wozniak of the biography, iWoz (WW Norton, 2005). Let us know what you think before Steve beats you to it. Good luck with that.

This is a challenge for readers. And all the non-math geeks among us.

If you’re wondering if you are even a math geek at all, click here.


  • Ant Pruitt

    I LOVE the Vi Hart youtube channel! My fav video of hers is the “Binary Hand Dance”.

    Which brings me to my point, my brain only thinks in black and white or for this instance, BINARY. No grey area. :)

    Not going to dig into 1/2 or 1/2 way or .999999999 stuff. Vi does make some great points, though. In other words, don’t argue with Vi. :)

    -RAP, II

  • Harsh Thaker

    Between 0 and 1, in math, we consider there are infinite float numbers. If you’ll consider the real objects to prove this thing with float numbers, it will never work. It would be like we start our journey from zero in order to reach at 1 ! If it never reaches to 1 then 0.9999999999 = infinite !

    So, 0.9999 != 1

  • Arlo James Barnes

    Well, I think Vi’s main channel’s main purpose is to present mathematics-related topics and the arguments surrounding them, so I do not know if they are solely ‘her’ arguments in this case – they have been presented before many times.
    And the video as a whole is more complex than the title suggests, she shows how either side has a good point and some interesting maths behind each perspective, but one is more appropriate considering conventional algebras.

  • Gina Smith

    She does a great job with this, no question.

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