The least score you need on the last test to get a B is 42.

This score ensures that the average of your five test scores is at least 80 but less than 90, which meets the requirement for a B grade.

Would you like more details or have any other questions?

Here are 5 related questions:

1. What is the range of scores that would give you a B on the last test?
2. How would the required score change if your other test scores were lower?
3. What is the minimum score needed to get an A if the requirement is an average of 90 or above?
4. How would the result change if the scoring system was different (e.g., weighted averages)?
5. What would happen if the last test was worth twice as much as the others?

Tip: When dealing with averages, always ensure that your final calculation checks both the lower and upper bounds if you are working within a range.