Answer:
The third reading must be between 6.3 and 8.1 inclusive.
Step-by-step explanation:
To find the average of three numbers, add the three numbers and divide by 3.
Let the third reading = p.
The average of the three readings is
This average must be between 7.2 and 7.8 inclusive. "Inclusive" means that the values 7.2 and 7.8 are allowed. That means the average must be greater than or equal to 7.2 and less than or equal to 7.8. We can write this as the following inequality.
Simplify the numerator.
Multiply the three sides by 3.
Subtract 15.3 from the three sides.
Answer: The third reading must be between 6.3 and 8.1 inclusive.