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# d r t help?

Lisa traveled to her cabin on the lake and back. The trip there took five hours and the trip back took six hours. She averaged 45 km/h on the return trip. Whats the average speed of the trip there?

### 3 Answers by Expert Tutors

Sally T. | Specializing in SAT PreparationSpecializing in SAT Preparation
4.9 4.9 (60 lesson ratings) (60)
1
Anytime you know two of the three variables you can calculate the third! So you are trying to find the average speed for the trip there, and you know the time but not the distance. Presumably the distance is the same in both directions, so we can calculate that from the return trip.

Since the distance = rate * time, we know the rate was 45 km/h and the time was 6 hours, so the distance is 45km/h * 6h = 270 kilometers. For the trip back, we know that rate = distance / time = (270 km/h ) / 5 hours = 54 kilometers per hour.

Don't let it throw you when the problem does not seem to have enough information; you can calculate the information you need from what has been given.

Good luck!

Hi Sally, 45 km/h is the average of the trip back, so the distance is 45km/h *6h=270km.
Yajing L. | Ph.D student from Colorado State UniversityPh.D student from Colorado State Univers...
1
The length of the trip is 45km/h*6h=270km, so the average speed of the trip is 270km/5h=54km/h.
Steve S. | Tutoring in Precalculus, Trig, and Differential CalculusTutoring in Precalculus, Trig, and Diffe...
5.0 5.0 (3 lesson ratings) (3)
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Lisa traveled to her cabin on the lake and back. The trip there took five hours and the trip back took six hours. She averaged 45 km/h on the return trip. Whatâ€™s the average speed of the trip there?

r1 = avg speed to cabin

5 hrs = time to cabin

6 hrs = time back

45 km/hr = avg speed back

d = distance to cabin

d = 5 r1

d = 45(6)

5 r1 = 45(6)

r1 = 45(6)/5 = 9(6) = 54 km/hr