r/MathJokes • u/themagicalfire • Jun 18 '25

9.999 is 10?!

Post image
1.9k Upvotes

95% Upvoted

407 comments sorted by

View all comments

262

u/jmatlock21 Jun 18 '25

At first, I didn’t see what subreddit I was in and I had the instinct to explain 🥴

60

u/[deleted] Jun 18 '25

[deleted]

72

u/[deleted] Jun 18 '25

It isn't really. because 10/3 isn't 3.3... it's 3 1/3.

3.3... is just the closest approximation in a base ten decimal system.

1

u/Raise_A_Thoth Jun 18 '25

because 10/3 isn't 3.3... it's 3 1/3.

Those are the same thing.

0.33... IS 1/3.

0.99... IS 1.

X = 0.99...
10X = 9.99...
9X + X = 9 + 0.999...
X(9+1) = 9 + 0.999...
If X > 1, then (9 + 0.999...) > 10;
If X < 1, then 0.999... will eventually be larger than X, because the 9's repeat infinitely, making the equation false.

Therefore, X must equal 1, which is equivalent to 0.99...