SOLUTION: roy drives to work at 70 mph and home that night along the same route at 30 mph. what is his average speed ?

Question 200669: roy drives to work at 70 mph and home that night along the same route at 30 mph.
what is his average speed ?
Answer by vleith(2983) (Show Source): You can put this solution on YOUR website!
Careful here. The kneejerk answer is (70+30)/2 = 50
But is not correct.
Why?
Sure the distance both way is the same, but the time required to cover that distance is less going 70 than it is at 30.
Let the distance be given as D
The total distance is 2D.

So we need to find out how much time is spent on the trip each way

Thus, becaue the return trip takes over twice as long as getting to work, the average speed is well less than the kneejerk answer.
Make sure you understand this concept. A problem just like this was on every SAT/GRE test I ever took.

RELATED QUESTIONS
Sally drives to work at an average speed of 47 mph and returns along the same route at a... (answered by Alan3354)

If I drive to work at 40 mph and return home along the same route at 50 mph, what is... (answered by ewatrrr,Alan3354)

A man drives to work at 40mph. He drives home,along the same route, at 60mph. What is his (answered by Alan3354)

Helen drives from her house to a store at 25 mph. She drives back along the same route at (answered by amoresroy)

Due Nov. 16 Helen drives from her house to the store at 25 miles per hour (mph).... (answered by user_dude2008)

Tahir travels from A to B at a speed of 40 mph, and returns along the same route a speed... (answered by bucky)

a man drives to his office at 60km/hr and returns home along the same route at 30km/hr.... (answered by josgarithmetic,Alan3354)

Starting at home, Luis traveled uphill to the hardware store for 30 minutes at just 10... (answered by Alan3354)

erin drove home at an average speed of 45 mph. she returned home in the evening along the (answered by stanbon,RAY100)