SOLUTION: 93. A car travels the first one-third of a certain dis-.tance with a speed of 10 km/hr, the next one-third distance with a speed of 20 km/hr and the last one-third distance with a

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: 93. A car travels the first one-third of a certain dis-.tance with a speed of 10 km/hr, the next one-third distance with a speed of 20 km/hr and the last one-third distance with a       Log On

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Question 840590: 93. A car travels the first one-third of a certain dis-.tance with a speed of 10 km/hr, the next one-third distance with a speed of 20 km/hr and the last one-third distance with a speed of 60 km/ hr. The average speed of the car for the whole journey is
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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A car travels the first one-third of a certain distance with a speed of 10 km/hr,
the next one-third distance with a speed of 20 km/hr
and the last one-third distance with a speed of 60 km/ hr.
The average speed of the car for the whole journey is
:
let a = the average speed for the trip
write a time equation; time = dist/speed; assume the total dist = 3
1%2F10 + 1%2F20 + 1%2F60 = 3%2Fa
multiply eq by 60a, cancel the denominators and you have
6a + 3a + a = 60(3)
10a = 180
a = 180/10
a = 18 km/hr is the average for the trip