What is the probability that a 3-digit positive integer picked at random will have one or more 7 in its digits?

A three digit number can be chosen in 9*10*10 = 900ways

No. of ways to choose a three digit number without 7 is 8*9*9 = 648 ways

probability of picking a three digit number that includes atleast one digit that is 7 is 1- (648/900) = 252/900 = 7/25