### 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

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