Mr Earl Bird leaves his house for work at exactly 8:00 A.M. every morning. When he averages a speed of 40 miles per hour, he is three minutes late to work. When he averages a speed of 60 miles per hour, he reaches three minutes early. At what average speed, in miles per hour, should Mr.Bird drie to arrive at his workplace precisely on time?

Solution:

The distance is x

x/40- x/60 = 1/10

So

x = 12 mile

So t=12/40 -3/60 = 15 min

12/V = 15 min

V=48

So the average speed should be 48 mph