SOLUTION: A train averaged 80 km/h for the first half of its trip. How fast must it travel for the second half of the trip in order to average 96 km/h for the whole trip? The answer is su

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Question 112984This question is from textbook Algebra and Trigonometry Structure and Method Book 2
: A train averaged 80 km/h for the first half of its trip. How fast must it travel for the second half of the trip in order to average 96 km/h for the whole trip?
The answer is supposedly 120 km/h, but no matter what I do I get 112 km/h!
Help would be greatly appreciated. (: This question is from textbook Algebra and Trigonometry Structure and Method Book 2

Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!
Let's let x = the speed for the second half of the trip. So %2880%2Bx%29%2F2 should be the average for the the whole trip. Now we can write:

%2880%2Bx%29%2F2=96

So let's solve for x:

80%2Bx=2%2A96=192
x=192-80
x=112

Seems you are right with your 112km/hr answer. I'm not sure where you got the 120 answer, but it is clearly incorrect. If you got it from the answers in the back of your textbook, it could still be wrong. Wouldn't be the first math book I've seen with errors in it.

Hope this helps.
John