An IQ test consists of 80 multiple choice questions. A question is selected at random. Find the probability that the question number contains exactly one '7'
There are a total of 80 questions, and 10 of them contain the number 7 (7, 17, 27, ..., 77).
To find the probability of selecting a question number with exactly one '7', we need to calculate the number of favorable outcomes and divide it by the total number of possible outcomes.
The number of favorable outcomes is 9, as there are 9 question numbers with exactly one '7' (7, 17, 27, 37, 47, 57, 67, 70, 71, 72, 73, 74, 75, 76, 78, 79).
The total number of possible outcomes is 80.
Therefore, the probability of selecting a question number with exactly one '7' is:
Probability = Number of Favorable Outcomes / Total Number of Possible Outcomes
Probability = 9 / 80
Probability = 0.1125
So the probability that the question number contains exactly one '7' is 0.1125 or 11.25%.