640 Measurement and Proportional ReasoningConvert Rates
WALKING Marvin walks at a speed of 7 feet per second. How
many feet per hour is this?
You can use 60 seconds = 1 minute and 60 minutes = 1 hour to
convert the rates._7 ft1 s = _7 ft1 s · _1 min60 s · _60 min
1 h
Multiply by _1 min60 s and _60 min1 h.= _^ 7 ft1 s · _1 min60 s · _60 min
1 h
Divide out common units.= _^7 ·^60 · 60 ft
1 · 1 · 1 h
Simplify.=
25,200 ft
_
1 h
Simplify.Marvin walks 25,200 feet in 1 hour.b. TRAINS An AMTRAK train travels at 125 miles per hour.
Convert the speed to miles per minute.Convert Derived Units
IDITAROD The Iditarod Snow Dog Race is a famous race in
Alaska in which mushers and their dog teams compete. The
average speed of the team is about 10 miles per hour. What is
this speed in feet per second?
We can use 1 mile = 5,280 feet, 1 hour = 60 minutes, and
1 minute = 60 seconds to convert the rates._10 mi
1 h
= _10 mi
1 h
·
5,280 ft
_
1 mi
· _1 h
60 min
· _1 min
60 sMultiply by distance and
time unit ratios.= _10 mi
1 h
·
5,280 ft
_
1 mi
· _1 h
60 min
· _1 min
60 s
Divide out common units.=
__^10 · 5,280 ·^1 · 1 ft
1 · 1 · 60 · 60 s Simplify.
=
_52,800 ft
3,600 s Simplify.
= _14.7 ft1 s Simplify.The Iditarod mushing teams travel at an average speed of
14.7 feet per second.c. RUNNING Charlie runs at a speed of 3 meters per second. About
how many miles per hour does Charlie run?Unit Rates Unit Rates Make sure the
units cancel so that the
desired units remain.639_648_C11_L1_895130.indd 640 12/31/09 9:07 AM