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A certain telephone number has 7 digits.If the
telephone number has the digit 0 exactly three times
and number one is not used at all what is the
probability that phone number contains 1 or more prime
eliminate three digits because 3 are zero. so last four digits could be 2,3.,4,5,6,7,8,9 for a totatl of 8^4 choices. Prime numbers are 2,3,5,7 so favorable outcomes are 4^4. so answer (hopefully)is 4^4/8^4.