Question 1117285: a university assinngs a 4 digit identification code what is the proabality that code doesn't contains 7? Answer by ikleyn(52776) (Show Source):
Since otherwise is not stated, I will assume that all 10 digits from 0 to 9 are allowed for all positions and repeating of digits is allowed.
Then the total number of all possible codes is equal to (each of ten digits is allowed in each of 4 positions).
The number of codes that do not the digit of 7 in any of 4 positions is (9 digits in each of 4 positions).
Therefore the probability under the question is = = 0.6561 = 65.61%.
