Question 369388
d=rt

d=25t ----> t = d/25
d=35t ----> t = d/35
d=40t ----> t = d/40
d=20t ----> t = d/20





average speed = total distance/total time = 4d/(d/25+d/35+d/40+d/20) = 5600/201 = 27.8606 mph


Answer: 28 mph