A car travels from point A to point B at an average speed of

A car travels from point A to point B at an average speed of 55mi/h and returns at an average of 50 mi/h. If the round trip takes 7h, find the distance between A and B. Please explain.

Solution

We know that

Average speed during the whole journey = ( 2xy) / ( x + y )

Given that

Let x = 55 mi/h

y = 50 mi/h

Time t = 7 h

Then

   Average speed during the whole journey = ( 2 x 55 x 50) / ( 55 + 50 )

= 5500 / 105

= 52.381 mi/h

Total distance travelled in 7 h = 52.381 mi/h x 7 h

= 366.667 mi

Distance between A an B = 366.667 / 2

= 183.334 mi

Therefore,

  Distance between A an B = 183.334 mi