How fast must he travel for the second half of the trip?
A truck travels 15 mph for the first half of the distance of a trip. The driver wants to average 30 mph for the whole trip. How fast must he travel for the second half of the trip?
pier_haringsma is correct. You do not need any additional information. Let
D = total distance of the trip
D/2 = the distance the driver has gone so far
T1 = amount of time he took to travel the first half of the trip
T2 = the complete length of time of the whole trip (both halves).
Now, he wants the average ( D / T2 ) to equal 30. His average so far is ( (D/2) / T1 ) = 15.
D/T2 = 30, so D = 30*T2
(D/2) / T1 = 15, so D = 30*T1
D = 30*T1 = 30*T2, so T1 = T2.
So the driver wants the total time for the trip (BOTH halves), T2, to equal the time for the first half of the trip, T1. This means he would have to travel the second half of the trip in no time, which is impossible.
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