SOLUTION: A car travels from A to B. First half of the distance it moves with a speed 60 mph, and the second half - with a speed 40 mph. Find the average speed of a car for the whole trip.

Question 216188: A car travels from A to B. First half of the distance it moves with a speed 60 mph, and the second half - with a speed 40 mph. Find the average speed of a car for the whole trip.
Answer by nerdybill(7384) (Show Source): You can put this solution on YOUR website!
A car travels from A to B. First half of the distance it moves with a speed 60 mph, and the second half - with a speed 40 mph. Find the average speed of a car for the whole trip.
.
Applying the "distance formula" (d=rt):
.
Let x = total distance from A to B
then
"time traveled 1st half" = (x/2)/60 = x/120
"time traveled 2nd half" = (x/2)/40 = x/80
.
Total time: x/120 + x/80
.
Average speed is
"total distance"/"total time"
= x/(x/120 + x/80)
Dividing numerator and denominator by 'x':
= 1/(1/120 + 1/80)
= 10/(1/12 + 1/8)
= 10/(2/24 + 3/24)
= 10/(5/24)
= 240/5
= 48 mph

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