kaplan的题

A certain telephone number has 7 digits. If he telephone number has the digit 0 exactly three times, and the number one is not used at all, what is the probability that the phone number contains 1 or more prime digits?
答案是1-（4/8）^4=15/16, 如果按一般的解法1-（分子/总数）应该怎么做呢？好难