SOLUTION: eric drove from town A to town B. after travelling 1/3 of the journey at an average speed of 75 km/hr, he continued to travel another 300 km to reach town b, if the average speed f

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Question 703164: eric drove from town A to town B. after travelling 1/3 of the journey at an average speed of 75 km/hr, he continued to travel another 300 km to reach town b, if the average speed for the whole journey was 90 km/hr, find his average speed for the last 2/3 of the journey?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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Eric drove from town A to town B.
After traveling 1/3 of the journey at an average speed of 75 km/hr, he continued to travel another 300 km to reach town b.
If the average speed for the whole journey was 90 km/hr, find his average speed for the last 2/3 of the journey?
:
From the given information, 2/3 = 300 km, therefore 1/3 = 150 km
Total distance = 450 km
:
Write a time equation, time = dist/speed
:
let s = the average speed for 2/3 of the journey
:
:1/3 time + 2/3 time = total time
150%2F75 + 300%2Fs = 450%2F90
reduce the fractions
2 + 300%2Fs = 5
300%2Fs = 5 - 2
300%2Fs = 3
3s = 300
s = 100 km/hr for 2/3 the journey
:
:
Check this using the time equation
150%2F75 + 300%2F100 = 450%2F90