SOLUTION: Hi after travelling 4/9 of her journey at 80km per hour, alice increased her speed to 100km per hour and took another 4 hours to complete her journey. What her average speed fo

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Question 1124328: Hi
after travelling 4/9 of her journey at 80km per hour, alice increased her speed to 100km per hour and took another 4 hours to complete her journey. What her average speed for the journey.
Thanks
Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
              SPEED      TIME          DISTANCE

part 1          80      (4d/9)(1/80)     4d/9

part 2         100         4             5d/9


100%2A4=5d%2F9
400%2A%289%2F5%29=d
highlight%28d=720%29---------the whole journey

-
%284%2A720%2F9%29%281%2F80%29
4%2A80%2F80
highlight%284%29----------time, hours, for part 1.
This means total time was 8 hours.

Journey's average speed: %28720%2F8%29%28km%2Fhour%29=highlight%2890%28km%2Fhour%29%29