(3 hours)(60 mph)+(5 hours)(24 mph)=300 total miles
(300 total miles)/(8 total hours)=37.5 mph average speed

The question has been answered nicely already, so I won't get into that.

However, if you're not sure how to proceed with the questions or you're pressed for time, you can get to a 50-50 guessing situation in about 10 seconds.
IF Jim traveled at 60 mph for the SAME amount of time that he traveled at 24 mph, then the average speed would be the average of 60 and 24.
That is, if he had spent the same time driving at each speed, his average speed WOULD HAVE been 42 mph, since (60+24)/2 = 42

HOWEVER, since Jim actually spent MORE TIME driving at 24mph, his average speed will be closer to 24mph than to 60mph.
In other words, his average speed will be LESS THAN 42 mph
This means the correct answer is either A or B.
Guess and move on.

Cheers,
Brent
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tIME = 3 S=60 d=ST = 60*3 =180 miles
time 2 = s=24 d st = 120 Miles

Total d = 180+120 =300
Total time =5+3= 8

Total Avg speed = Total Distance / total time = 300/8 = 37.5 or B