SOLUTION: When travelling at (x-5) km/h, a train takes 2x hours to travel 12km. Find the speed of the train.

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Question 1118152: When travelling at (x-5) km/h, a train takes 2x hours to travel 12km. Find the speed of the train.
Found 2 solutions by josgarithmetic, greenestamps:
Answer by josgarithmetic(39616) About Me  (Show Source):
You can put this solution on YOUR website!
RT=D for R rate, T time, D distance.
Your example uses R=x-5, and T=2x, and D=12.

highlight_green%2812%2F%282x%29=x-5%29

6%2Fx=x-5

x%5E2-5x=6

x%5E2-5x-6=0
%28x-6%29%28x%2B1%29=0
highlight_green%28x=6%29
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Speed was highlight%281%29 kilometer per hour.
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check:
recall, x=6.
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12%2F%282x%29=x-5
12%2F%282%2A6%29=6-5
12%2F12=1
1=1
(speed given as x-5;
which is evaluated as 1 )

Answer by greenestamps(13198) About Me  (Show Source):
You can put this solution on YOUR website!


Distance = rate times time:

12+=+%28x-5%29%282x%29

6+=+%28x-5%29%28x%29 (note this is equivalent to taking the given information, that the train travels 12 km in 2x hours, and by simple logic changing it to having the train travel 6 km in x hours)

6+=+x%5E2-5x
x%5E2-5x-6+=+0
x-6%29%28x%2B1%29+=+0

The train's speed is either 6 km/hr or -1 km/hr; I think we can rule out the negative speed....