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July 8th, 2018, 10:27 PM  #1 
Senior Member Joined: Aug 2014 From: India Posts: 343 Thanks: 1  How to solve this problem?
Two pipes A and B are connected to a tank. A can fill the tank with 80% pure milk in 7 hours, while B can fill the tank with 90% pure milk in 3 hours. What will be the purity of the milk in the tank if both the pipes are opened together to fill the empty tank? Solution: A is 80% and B is 90%. Here B is filling the tank fast. I can't proceed from here. please help me. 
July 9th, 2018, 01:48 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 20,464 Thanks: 2038 
The "fillingratio" of the pipes is 3:7, so pipe A supplies 3/(3 + 7) = 30% of the tank's capacity, and pipe B supplies 70% of the tank's capacity. Hence the purity that results will be 80% of 30% + 90% of 70% = 87%. 
July 9th, 2018, 03:31 PM  #3 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,277 Thanks: 1023 
Hey Skip, you told me recently not to give out full solutions.....???? Here: Why 4:7 is not the answer? Last edited by Denis; July 9th, 2018 at 03:34 PM. 
July 10th, 2018, 12:02 AM  #4 
Global Moderator Joined: Dec 2006 Posts: 20,464 Thanks: 2038 
The opening post there contained "Please don't post the final answer."

July 10th, 2018, 04:13 AM  #5 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,277 Thanks: 1023 
I give up...


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