A way to work it.

The track is 1 mile in length.

At 90 mph how many laps (it's a 1 mile track) will Bobby make in 1 hour?

You should say 90.

If he only drives for 1/2 hour, how many miles?

If he drives for 1/10 of an hour, how many miles?

At 90 mph how long will it take Bobby to make 1 lap around the track? <-- key question.

Call this answer T1.

How long will it take Bobby to make 2 laps around the track? <-- IMPORTANT ANSWER

Call this answer T2

How long will it take Bobby to make 10 laps around the track? <-- Bobby's TOTAL time on the course.

Call this answer T3

Rick will be on the track for how long.

Since he will complete the course the same time as bobby, Rick's time must be T3-T2.

Call that time t

Distance = Rate x Time

Bobby's speed

10 miles = Z mph x t hours

(omitting the units of measure)

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