How much time does the man take in driving to and from the shopping center?

A man drives from his home at 30 miles per hour to the shopping center which is 20 miles from his home. On the return trip he encounters heavy traffic and averages 12 miles per hour. How much time does the man take in driving to and from the shopping center?

MetroEye: The average speed = \(\dfrac{Distance travelled}{Time Taken}\)

Time taken for the to-travel = \(\dfrac{20 miles}{30 miles per hour}\)

Time taken for the from-travel = \(\dfrac{20 miles}{12 miles per hour}\)

Total time = \(\dfrac{20}{30}\) + \(\dfrac{20}{12}\) = \(\dfrac{2}{3}\) + \(\dfrac{5}{3}\) = \(\dfrac{7}{3}\) hours = \(\dfrac{7}{3}\) * 60 = 140 minutes = 2 hour 20 minutes

The man took 2 hours 20 minutes in driving to and from the shopping center.

Average speed for the entire trip?

A motorist made a 60 mile trip averaging 20 miles per hour. On the return trip, he averaged 30 miles per hour. What is the motorist's average speed for the entire trip?

Average speed = Total distance travelled / Total time taken

Total distance for the trip = 60+60=120 miles
Total time taken for the trip = 60/20+60/30=3+2=5 hours.

So the average speed = 120/5=24 mph.

Motorist's average speed for the entire trip is 24 miles per hour.