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Question 109146: A pool can be filled by one particular pipe in 10h, whereas a different pipe requires 6 h to fill the pool. How long would it take to fill the pool with both pipes turned on? Leave you answer in decimal form.
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An airplane flies 725 mi with the wind. In the same amount of time it can fly 675 mi against the wind. The speed of the plane in still air is 280 mph. Find the speed of the wind.
Answer by edjones(8007)   (Show Source):
You can put this solution on YOUR website! 1st pipe fills 1/10 the pool in 1 hr
2nd pipe fill 1/6 the pool in 1 hr
Together: 1/10 + 1/6
=3/30 + 5/30
=8/30
=4/15 of the pool filled in 1 hr or:
15/4= hrs until pool filled
= 3 3/4 hrs
= 3.75 hrs
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st=d, s=speed, t=time, d=distance
Let x be speed of the wind
t(280+x)=725
t=725/(280+x)
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t(280-x)=675
t=675/(280-x)
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Since the t's are equal:
725/(280+x)=675/(280-x)
725(280-x)=675(280+x) multiply both sides by (280-x)(280+x) to eliminate fractions.
203000-725x=189000+675x
14000=1400x add 725x-189000 to each side.
x=10 mph wind speed
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Check:
t=725/290=2.5 hrs
t=675/270=2.5 hrs
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Ed
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