aiming4mba wrote:
A car travels from point A to point B. The average speed of the car is 60 miles/hr and it travels the first half of the trip at a speed of 90 mi/hr. What is the speed of the car in the second half of the trip?
A. 30
B. 45
C. 60
D. 75
E. 90
We can use the formula:
average = total distance/total time
Let’s denote the total distance by d and the unknown speed of the car in the second half of the trip by r.
60 =d/[(d/2)/90 + (d/2)/r)]
60 =d/[d/180 + d/2r]
60[d/180 + d/2r] = d
d/3 + 30d/r = d
1/3 + 30/r = 1
30/r = 2/3
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