Embarking on a road trip, you hope to average a speed of 90.0 km/hr. Driving through bad weather, you finally reach the midpoint (half the distance) of your trip, but realize that you have only been averaging 5.0 X 10^1 km/hr. How fast would you have to drive the second half of the trip to keep your desired arrival time? *

Explanation:

average speed = 90 km / hr

Let the total distance be 2 d .

time required to cover the time = 2 d / 90

time taken   to cover distance d at 50 km /h = d / 50

time required to cover the  nd half = 2 d / 90 -  d / 50

.02222 d  - .02 d = .002222 d

speed required = d/2 / .002222d

1 / 2 x .002222

= 225 km /h .

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