Question 930804:  The speed of a moving sidewalk is 4 ft/sec. On the moving sidewalk a person can walk 99 feet forward in the same time it takes to walk 17 ft on a non-moving sidewalk in the opposite direction. At what rate would a person walk on a non-moving sidewalk? 
 Answer by TimothyLamb(4379)      (Show Source): 
You can  put this solution on YOUR website! x = walking speed on a non-moving sidewalk 
y = speed of moving sidewalk = 4 ft/sec 
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s = d/t 
t = d/s 
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moving sidewalk: 
t = 99/(x + y) 
t = 99/(x + 4) 
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non-moving sidewalk: 
t = 17/x 
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equate times: 
99/(x + 4) = 17/x 
99/(x + 4) - 17/x = 0 
99x/x(x + 4) - 17(x + 4)/x(x + 4) = 0 
99x - 17(x + 4) = 0*x(x + 4) 
99x - 17x - 4*17 = 0 
82x - 68 = 0 
82x = 68 
x = 68/82 
x = 0.829268292683 ft/sec 
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check: 
t = 99/(x + 4) 
t = 99/(0.829268292683 + 4) 
t = 20.5 sec 
-- 
t = 17/x 
t = 17/0.829268292683 
t = 20.5 sec 
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answer: 
x = walking speed on a non-moving sidewalk = 0.829268292683 ft/sec 
x = walking speed on a non-moving sidewalk = 0.829 ft/sec * (1/5280 mile/ft) * (60*60 sec/hr) 
x = walking speed on a non-moving sidewalk = 0.57 mph 
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