word problem:

The Rory family drove 310 miles each day for 4 days. Then on Friday they drove 250 miles to Centerville. On Saturday they drove 150 miles to Westfield. What else do you need to know to determine how many miles they averaged each day for that one week?
a) number of miles driven back home
b) number of days in a week
c) distance from Centerville to Westfield
d) number of miles driven on the seventh day.

I picked d.
is that right?

Right.

No, the correct answer is b) the number of days in a week.

To determine the average number of miles the Rory family drove each day for that one week, we need to know the total distance they drove for the entire week and then divide it by the number of days they drove.

In this scenario, we are given the distances driven on each individual day, but we don't know the total number of days they drove. Without knowing the number of days in a week, we can't calculate the average distance. Therefore, b) the number of days in a week is needed to determine the average distance per day.