Question

Sam drove for 2 hours at 45 mph. He has the same distance remaining. How fast should he drive to make his average speed 60 mph?

Answer 1

Sam needs to drive at 90 mph to make his average speed 60 mph

It is given that Sam drove for 2 hours at 45mph.

So, distance covered = Speed * Time

= 45*2 miles

= 90 miles

He needs to cover the remaining 90 miles at a speed so that the average speed becomes 60 mph.

So, total distance to be covered in the journey = 90 + 90 = 180 miles.

Speed he desires as an average = 60 mph.

Time = Distance/Speed = 180/60 = 3 hours.

In 3 hours he needs to cover the entire journey. Out of it, 2 hours is taken to cover the first 90 miles.

The next 90 miles he needs to cover it at = (3-2) hours = 1 hour

So, distance to be covered = 90 miles.

Time = 1 hour

Speed = Distance/Time = 90/1 = 90mph.

90 mph is the required answer.