Calvin was making a trip to the University of Chicago. When he drove down, he took Lakeshore Drive, and averaged 35 miles per hour. On his way back, he took the I-94 highway, and averaged 50 miles per hour. Given that the return journey was 4 miles longer and took 6 minutes less, what is the length of the Lakeshore Drive route (in miles)?
distance = speed*time
35t+4 = 50(t-.1)
t = .6 hrs
35(.6) = 21 miles
check:
(21)/35 = 3/5 = .6 hrs = 36 min
(21+4)/50 = 1/2 = 30 min