Brain Teasers
Crazy Math
prove the following:
3.99999... = 4
(by using '...' i mean that the 9's are repeating)
3.99999... = 4
(by using '...' i mean that the 9's are repeating)
Answer
3.9999... = X3.9999... * 10 = 39.9999.... = 10X
10X - 3.9999... = 9X
39.9999... - 3.9999... = 36 = 9X
36 / 9 = 9X / 9 = 4
therefore, X = 4
Hide Answer Show Answer
What Next?
View a Similar Brain Teaser...
If you become a registered user you can vote on this brain teaser, keep track of which ones you have seen, and even make your own.
Solve a Puzzle
Comments hidden to avoid spoilers.
Follow Braingle!