For the first 5 hours of a trip, a plane averaged 120 kilometers per hour. For the remainder of the trip, the plane traveled an average speed of 180 kilometers per hour. If the average speed for the entire trip was 170 kilometers per hour, how many hours long was the entire trip? A. 15B. 20C. 25D. 30E. 35

Option D is the correct answer.

Step-by-step explanation:

For the first 5 hours of a trip, a plane averaged 120 kilometers per hour.

Distance traveled in first 5 hours = 5 x 120 = 600 km

Let the remainder time be t hours.

For the remainder of the trip, the plane traveled an average speed of 180 kilometers per hour.

Distance traveled in remaining hours = 180 x t = 180t

Total distance traveled = 600 + 180t

Total time taken = 5 + t

Average speed of entire journey = 170 km/hr

We have

Total distance traveled = Average speed of entire journey x Total time taken

600 + 180t = 170 x (5+t)

600 + 180t = 850 + 170t

10t = 250

t = 25 hours

Total time taken = 5 + 25 = 30 hours

Option D is the correct answer.