Answer:
C. 1000/x + 5000/(2x -10)
Explanation:
You want the total time a climber spent when he climbed 1000 feet at x feet per hour, and 5000 more feet at (2x -10) feet per hour.
Time
The relation between time, speed, and distance is ...
time = distance / speed
The total time is the sum of the times for the two distances.
First time
The time for 1000 ft at x feet per hour is ...
time 1 = 1000/x
Second time
The rate for the second part of the climb was 10 ft per hour less than twice the first rate, so was ...
2x -10
Then the time for 5000 ft at this rate is ...
time 2 = 5000/(2x -10)
Total time
The total time spent climbing was ...
total = time 1 + time 2
total = 1000/x + 5000/(2x -10) . . . . . . matches choice C
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Additional comment
The relation between speed, time, and distance is usually seen as ...
speed = miles per hour
As a fraction, this is ...
speed = distance / time
Above, we rearranged this to ...
time = distance / speed
It's just another form of the relationship ...
distance = speed × time
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