July 5th, 2018, 01:14 AM  #1 
Senior Member Joined: Aug 2014 From: India Posts: 343 Thanks: 1  Why 4:7 is not the answer?
The contents of two vessels containing water and milk in the ratio 3:5 and 7:8 are mixed in the ratio 4:7. What would be the ratio of water and milk in the final mixture? Please don't post the final answer. My doubt is: Why 4:7 is not considered as ratio of water and milk in the final mixture? 
July 5th, 2018, 03:07 AM  #2 
Senior Member Joined: Apr 2014 From: UK Posts: 891 Thanks: 328 
Why would you consider it without applying any maths to work it out?

July 5th, 2018, 03:23 AM  #3  
Senior Member Joined: Aug 2014 From: India Posts: 343 Thanks: 1 
That's not the way you should reply: Quote:
when you take four parts of solution 1 (3:5) and seven parts of solution 2 (7: 8 ) , and you then combine the two solution Then I will understand the question. Hope this helps!  
July 5th, 2018, 05:57 AM  #4 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,466 Thanks: 949  
July 5th, 2018, 06:14 AM  #5 
Senior Member Joined: Oct 2009 Posts: 610 Thanks: 187 
When you take four parts of solution 1 (3:5) and seven parts of solution 2 (7: 8 ) , and you then combine the two solution

July 5th, 2018, 08:21 AM  #6 
Senior Member Joined: Apr 2014 From: UK Posts: 891 Thanks: 328 
Ganesh, I was responding to your doubt, not the math question posed (because you did not want an answer to that). The point I was trying to make was that I completely fail to understand why you would consider that as a possible solution without showing any reason why it might possibly be true. 
July 5th, 2018, 08:23 AM  #7  
Math Team Joined: Jan 2015 From: Alabama Posts: 3,261 Thanks: 894  Quote:
 
July 5th, 2018, 10:16 AM  #8 
Global Moderator Joined: Dec 2006 Posts: 19,877 Thanks: 1834 
Consider a simpler problem. A mixture of 3 pints water and 5 pints milk is added to an equal volume (8 pints) of water. What is the ratio of water to milk that results? Clearly, the answer isn't 1:1. Instead, the resulting mixture has 11 pints water to 5 pints milk.

July 5th, 2018, 12:30 PM  #9 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,466 Thanks: 949 
The contents of 2 vessels containing water and milk in ratio 3:5 and 7:8 ... a=3, b=5 c=7, d=8 ....are mixed in the ratio 4:7. u=4, v=7 What would be the ratio of water and milk in the final mixture? r = ratio General case formula for 2 vessels: r = [u*a / (a+b) + v*c / (c+d)] / (u+v) = ? EDIT: answer removed... Last edited by Denis; July 5th, 2018 at 01:03 PM. 
July 5th, 2018, 12:50 PM  #10 
Global Moderator Joined: Dec 2006 Posts: 19,877 Thanks: 1834 
That comes far too close to posting the final answer.


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