Posted by **KK** on Wednesday, May 1, 2013 at 10:20pm.

A bicycle lock has a 4-digit combination. Each of the digits is a number from 0 to 9. Find the probability that the lock has a combination in which 3 of the 4 digits are 3s

- Math -
**Reiny**, Wednesday, May 1, 2013 at 10:38pm
I will assume that repeats are allowed as in most combination locks

so number of possible codes = 10^3 = 1000

So we want three 3's and one non-3

333x

33x3

3x33

x333---> where x is a number other than 3

so there are 4(9) of these or 36

so prob of our event = 36/1000 = 9/250

- Math -
**Jason**, Monday, May 12, 2014 at 12:18pm
Reiny was close, I would adjust the possible combination to 10^4 = 10,000

So 36/10,000 = 9/2,500

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