Math
posted by John .
To convert miles per hour to feet per second, which conversion factor would not be used?
a. 1 hr/60 min
b. 1 min/60 sec
c. 5280 ft/1 mi
d. 1 mi/5280 ft

To convert miles per hour to feet per second, which conversion factor would not be used?
a. 1 hr/60 min
b. 1 min/60 sec
c. 5280 ft/1 mi
d. 1 mi/5280 ft 
mi/hr * 1hr/60min * 1min/60sec * 5280ft/mi
Note that the units all cancel out, leaving ft/sec
Actually all of the factors will work, if you divide by 1mi/5280ft.
However, since one usually wants to multiply, I'd say (d) would not be used. 
yubfr