SOLUTION: A man normally takes 5 hours to travel at a certain speed from A city to B .one day, he increases his speed by 4 km/Hrs and finds that the journey from A to B takes half an hour

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Question 973026: A man normally takes 5 hours to travel at a certain speed from A city to B .one day, he increases his speed by 4 km/Hrs and finds that the journey from A to B takes half an hour less than the normal time. Find his normal speed.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +s+ = his normal speed in km/hr
Let +d+ = distance from A to B in km
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Traveling at normal speed:
(1) +d+=+s%2A5+
Traveling at faster speed:
(2) +d+=+%28+s+%2B+4+%29%2A%28+5+-+.5+%29+
--------------------------
(2) +d+=+%28+s+%2B+4+%29%2A4.5+
(2) +d+=+4.5s+%2B+18+
Substitute (1) into (2)
(2) +5s+=+4.5s+%2B+18+
(2) +.5s+=+18+
(2) +s+=+36+
His normal speed is 36 km/hr
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check:
(1) +d+=+s%2A5+
(1) +d+=+36%2A5+
(1) +d+=+180+ km
and
(2) +d+=+%28+s+%2B+4+%29%2A4.5+
(2) +d+=+40%2A4.5+
(2) +d+=+180+ km
OK