Question 384186
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Hi,         
Let x represent the time it would take to fill tank for all three working together.
Question states;  Per Hour the Equalizer:
 1/3 + 1/4 - 1/5 = 1/x  Multiplying each term by 60x so as all denominators = 1
 20x + 15x - 12x = 60
           23x = 60
             x = 60/23 hr 

  With all lines open how long until tank is 3/5 full         
  3/5 * 60/23 = 36/23 = 1.57 hrs, tank will be  3/5 full