Average Rate Problem: Solve for r=60mph

[carlodelmundo]

Homework Statement

Support you wish to average 40 mph on a trip and find that when you are half the distance to your distance to your destination you have averaged 30 mph. How fast should you travel in the remaining half of the trip to attain an overall average of 40 mph?

Homework Equations

d = rt

The Attempt at a Solution

I used S(avg) = x / (t1 + t2) = 40 mi/hr

I substituted (2d/60) for t1 and (d/2r) for t2.

Doing some algebraic manipulations, I got r = 60 mph. Is this correct?

 

[Mark44]

Homework Statement

Support you wish to average 40 mph on a trip and find that when you are half the distance to your distance to your destination you have averaged 30 mph. How fast should you travel in the remaining half of the trip to attain an overall average of 40 mph?

Homework Equations

d = rt

The Attempt at a Solution

I used S(avg) = x / (t1 + t2) = 40 mi/hr

I substituted (2d/60) for t1 and (d/2r) for t2.

Doing some algebraic manipulations, I got r = 60 mph. Is this correct?

Yes, and this is easy enough to check.

 

[carlodelmundo]

Thanks!