Question

S

If it takes someone t minutes to drive, run, or walk a mile, then their average speed s(t), in miles per hour, is

given by the formula

60

s(t) = 0

for t > 0

t

Find s(10) and s(12).

s(10) =

s(12) =

miles per hour

miles per hour

Answer 1

The average speed here is 60 mph.

Explanation:

We need to express the unit rate here. That's the speed, which is defined as (distance) / (time):

1 mile

speed s(t) = ----------------

t (min)

We need to convert the unit of time (min) to the new unit of time (hrs):

1 mile 60 min

speed s(t) = --------------- * -------------- = 60 miles/hr = 60 mph

t (min) 1 hr

The average speed here is 60 mph. This is not dependent on time, t, so we cannot calculate s(10) or s(12). Because of this, s(t) = 60 mph. The distance traveled in t hours is d(t) = s(t)*t.