Question

Today, Mariana is running a 10-mile race and using her watch to help with pacing. She will run at a steady pace of 9 minutes per mile, and so she expects to finish the race in 90 minutes. The function D(m) represents the distance Mariana has left to run, in miles, after m minutes.
What is the range of D(m)?
all real numbers from 0 to 10
all whole numbers from 0 to 90
all real numbers from 0 to 90
all whole numbers from 0 to 10

Answer 1

"All real numbers from 0 to 10."

At m = 0 she has 10 miles left and at m = 90 she has 0 miles left. Because she runs continuously, D(m) takes every real value between 10 and 0 (inclusive), i.e. all real numbers from 0 to 10.