SOLUTION: A motorist traveled from Town A to Town B. After traveling one third of the distance for the journey at an average speed of 45 km/h, he continued to travel another 480 km to reach

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Question 1030976: A motorist traveled from Town A to Town B. After traveling one third of the distance for the journey at an average speed of 45 km/h, he continued to travel another 480 km to reach Town B. If his average speed for the entire journey was 54 km/h, what was his average speed for at least two thirds of the distance?
Answer by ankor@dixie-net.com(22740) (Show Source):
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A motorist traveled from Town A to Town B.
After traveling one third of the distance for the journey at an average speed of 45 km/h, he continued to travel another 480 km to reach Town B.
If his average speed for the entire journey was 54 km/h, what was his average speed for at last two thirds of the distance?
:
From the information given we know the first third distance was half the distance of the last two thirds: 480/2 = 240km
The total dist: 240 + 480 = 720km
:
let s = speed for the last 2/3 dist
:
Write a time equation; time = dist/speed
:
Time at 45 + time at s = total time
+ =
multiply by the least common denominator, 270s
270s* + 270s* = 270s*
Cancel the denominators
6s(240) + 270(480) = 5s(720)
1440s + 129600 = 3600s
129600 = 3600s - 1440s
129600 = 2160s
s = 129600/2160
s = 60 km/hr for final 2/3 of the trip
:
;
See if that checks out
+ =
5.33 + 8 = 13.33 hrs