Question

Use the image to answer the question.

A coordinate plane for distance versus time.
▶Click for Long Desc

Riley is training to run a 5-mile race. The graph represents the distance (miles) she ran with respect to time (minutes) in her first training run. Over which time interval did she run the fastest, [0,8]
or [2,11]
? Justify your answer in 1–2 sentences.

Answer 1

On [0,8] the average speed = (4 − 0)/(8 − 0) = 4/8 = 0.5 miles/min.
On [2,11] the average speed = (5 − 1)/(11 − 2) = 4/9 ≈ 0.444 miles/min, so she ran fastest on [0,8].