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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?

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3 Answers

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)
"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 √

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