Typical DAT Math question

[dantheman2007]

Who can solve this?

A tank can be filled by a pipe in 30 min. and emptied by another pipe in 50 min. How many minutes will it take to fill the tank if both pipes are open?

Thank!

-Dan

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[Ex_EE]

I set the fill rate at 1 g/min and with it being 30 minutes that means 30 g. So, then I set up the equation with x being the time in minutes:
x - 3/5 X = 30
x = 75 minutes

 

[dantheman2007]

nice work, thanks

 

[Chga]

i found the common factor first
30 and 50 have 150 in common
150/30 = 5 units/min
150/50 = 3 units/min
5-3 = 2 units / min is the net gain
150 units / 2 units / min = 75 mins