trigonometry
posted by monic .
A truck with 48in.diameter wheels is traveling at 45 mi/h.
(a) Find the angular speed of the wheels in rad/min.
rad/min
(b) How many revolutions per minute do the wheels make?
rev/min

one rotation = 2π(48) = 96π inches
in 1 hour it goes 45 miles
= 45x5280x12 inches
= 2851200 inches
number of rotations per hour
= 2851200/(96π) = 9453.8.. rotations per hour
= 157.563 rpm
= 157.563x(2π) radians /min
= 990 radians/min 
45 mi/hr * 5280*12 in/mi /(2pi*48in/rev) * hr/60min * 2pi rad/rev = 3960 rev/min
rev/min = rad/min * rev/2pi rad, so divide 3960 by 2pi 
Oops. Off by a factor of 2. I was using a radius of 48 in

Rats, I read it wrong also
radius should have been 24 , not 48
make the necessary adjustments in the above.
(time to go to bed)