Question 97182
A tank can be filled by one pipe in 30 minutes & emptied by another in 50 minutes. If both pipes are open, how long will it take to fill the tank?
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Let x = time (in minutes) required, when both pipes are open, and they fill the tank
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Let the full tank = 1
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{{{x/30}}} - {{{x/50}}} = 1
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Multiply equation by 150 to get rid of the denominators, resulting in:
5x - 3x = 150
2x = 150
x = 150/2
x = 75 minutes required to fill the tank
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Check solution
{{{75/30}}} - {{{75/50}}}  = 
:
{{{5/2}}} - {{{3/2}}}  = 2/2 = 1
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