Final answer:
The 40th customer will be the first to receive both a free tire wash and a free coffee mug.
Step-by-step explanation:
To find out which customer will be the first to receive both a free tire wash and a free coffee mug, we need to determine the least common multiple (LCM) of 5 and 8. The LCM is the smallest number that is divisible by both 5 and 8.
To find the LCM, we can list the multiples of 5 and 8: 5, 10, 15, 20, 25, 30, ..., and 8, 16, 24, 32, ... We can see that the first number that appears in both lists is 40. Therefore, the 40th customer will be the first to receive both a free tire wash and a free coffee mug.