SOLUTION: A man made a 70-mile trip at a certain average rate. By increasing his average rate by 5 miles per hour, he traveled 80 miles in the same time that he spent on the 70-mile trip. Fi

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Question 195004: A man made a 70-mile trip at a certain average rate. By increasing his average rate by 5 miles per hour, he traveled 80 miles in the same time that he spent on the 70-mile trip. Find his average rate on each trip.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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A man made a 70-mile trip at a certain average rate.
By increasing his average rate by 5 miles per hour, he traveled 80 miles in
the same time that he spent on the 70-mile trip. Find his average rate on each trip.
:
Let s = the original speed (70 mi trip)
then
(s+5) = the speed required for the 80 mi trip
:
The two trips have equal time; write a time equation; Time = dist%2Fspeed
:
80 mi time = 70 mi time
80%2F%28%28s%2B5%29%29 = 70%2Fs
Cross multiply and you have:
80s = 70(s+5)
:
80s = 70s + 350
:
80s - 70s = 350
:
10s = 350
s = 350%2F10
s = 35 mph original speed
then
35 + 5 = 40 mph is the faster speed
;
:
Check solution by finding the time of each trip
70/35 = 2 hr
80/40 = 2 hr