To find the number of times the digit 9 appears in the list of all integers from 1 to 150, we can consider the following: 1. Count the number of times 9 appears as the units digit: It appears 15 times (9, 19, 29, ..., 149). 2. Count the number of times 9 appears as the tens digit: It appears 15 times (90, 91, 92, ..., 99, 109, 119, ..., 149). Therefore, the digit 9 appears a total of 15 + 15 = 30 times in the list of all integers from 1 to 150.
