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# A man completed a trip of 136 km in 8 hrs. Some part of the trip was covered at 15 km/hr. What is the part of the trip covered at 18 km/hr?

A man completed a trip of 136 km in 8 hrs. Some part of the trip was covered at 15 km/hr. What is the part of the trip covered at 18 km/hr?

### 3 Answers by Expert Tutors

Eric Y. | SAT PrepSAT Prep
5.0 5.0 (5 lesson ratings) (5)
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distance = rate * time

distance = distance15kmph + distance18kmph

136 km = 15kmph * (Time at 15) + 18kmph * (Time at 18)
Let Time at 18 = x
Assume no other driving speeds
Time at 15 is 8-x

136 = 15(8-x) + 18x
136 = 120-15x+18x
16 = 3x
x = 16/3 = 5.33 hr (5hour,20min)
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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"A man completed a trip of 136 km in 8 hrs. Some part of the trip was covered at 15 km/hr. What is the part of the trip covered at 18 km/hr?"

15 t1 + 18 t2 = 136
t1 + t2 = 8

Multiply 2nd eqn by -15 and add to 1st eqn:

15 t1 + 18 t2 = 136
-15t1 - 15t2 = -120
––––––––––––––––
0 + 3 t2 = 16

t2 = 16/3 = 5+1/3 = 5 hrs 20 min at 18 km/hr

t1 = 8 - t2 = 7 hrs 60 min - 5 hrs - 20min
t1 = 2 hrs 40 min at 15 km/hr

15 t1 = 15(2+2/3) = 40 km at 15 km/hr
18 t2 = 18(16/3) = 96 km at 18 km/hr

check: 40 + 96 = 136 √
Alex S. | Retired, Looking to Share My Love of Mathematics and ComputersRetired, Looking to Share My Love of Mat...
4.8 4.8 (75 lesson ratings) (75)
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X is time spent at 15 km/hr
y is time spent at 18 km/hr

x+y=8
15x+18y=136

15x+18*(8-x)=136
15x+144-18x=136
3x=8
x=8/3 hr = 2 hr 40 min
y=5 hr 20 min