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November 22nd, 2016, 11:26 AM  #1 
Newbie Joined: Nov 2016 From: United States Posts: 1 Thanks: 0  help solve problem
I have 30ml solution of 0.05%. How much water needed to add to make a solution of 0.04%? Once I have solution of 0.04%, how much water needed to add to make a solution of 0.03%? Thank you. Last edited by skipjack; November 22nd, 2016 at 01:08 PM. 
November 22nd, 2016, 11:59 AM  #2 
Math Team Joined: Jul 2011 From: Texas Posts: 2,097 Thanks: 972 
x = mL of pure water 30(.05) + x(0) = (30+x)(.04) solve for x, then substitute the calculated value for x in the following equation ... y = mL of pure water (30+x)(.04) + y(0) = (30+x+y)(.03) solve for y 
November 22nd, 2016, 01:22 PM  #3 
Global Moderator Joined: Dec 2006 Posts: 16,187 Thanks: 1145 
Is the original solution 0.05% or 5%?

November 22nd, 2016, 01:29 PM  #4 
Math Team Joined: Jul 2011 From: Texas Posts: 2,097 Thanks: 972  
November 22nd, 2016, 04:52 PM  #5 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 7,819 Thanks: 532 
It's this simple (w = water): .....30 @ 5 ......w @ 0 ======= 30+w @ 4 (30*5 + w*0) / (30 + w) = 4 

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