1976 bus....?

Question

if you have 19, four-hundred pound men, travleling in a 1976 model bus, going 85 miles per hour, and the bus sudenly slows to 35 miles per hour for 2 minutes because there is a bus member mooning another bus, what is the average speed of the bus if it travels for a total distance of 20 miles????

Answer 1

2 mins at 35 mph = (2 / 60) * 35 = 1.17 miles
The rest of the 20 miles at 85 mph
20 - 1.17 = 18.83 / 85 = 0.22 hours
avg speed = distance / time
s = 20 / (.22 + (2 / 60)) = 78.95 mph

Answer 2

Let d be the distance travelled during mooning:
d = 35 * 1/30 hour
d = 7/6 miles (1.1666...)

Let t be the time travelled while *not* mooning:
(20 - d) = 85 * t
18 5/6 = 85 * t
113/6 = 85 * t
t = 113/(6 * 85)
t = 0.221568627 hours

Total distance was 20 miles
Total time was 113/(6 * 85) + 1/30 = 0.254901961 hours

Average rate = 20 / 0.254901961
≈ 78.46 mph

Answer 3

DanE's answer assumes, of course, that the speed changed instantaneously from 85 MPH to 35 MPH (and possibly back to 85 MPH) ;)

Without this assumption it's impossible to answer the question because we don't know the rate of acceleration/deceleration.

Oh, and for the record, the number and weight of the passengers, as well as the vehicle details, are simply red herrings to make the problem seem more complex.