<p>What is the probability that a number chosen at random from the integers greater than 9 and less than 100 will have 7 as at least one of its digits?</p>
<p>I couldn't find it in google, and I don't have the answer. So can anyone please tell me if I'm right:</p>
<p>70-79 10 numbers with 7 as at least one of the digits
10-99 9 numbers with 7 as at least one of the digits</p>
<p>So, 10+9-1(77 is the intersection) = 18. Probability would be 18/90 = 1/5. Is this correct?</p>