SOLUTION: How much pure water must be mixed with 8 pints of 70% developer to produce a mixture that is 11% developer?

Question 86237: How much pure water must be mixed with 8 pints of 70% developer to produce a mixture that is 11% developer?

Answer by checkley75(3666) (Show Source): You can put this solution on YOUR website!
THE SECRET FOR THESE TYPE OF SOLUTION PROBLEMS IS TO CONCENTRATE ON THE AMOUNT OF THE MIXTURE. 8 PINTS HAS A MIX OF 70% THUS WE HAVE .7*8=5.6 PINTS OF DEVELOPER. THE ADDED WATER HAS NO DEVELOPER. SO WE ADD 0*X PINTS OF DEVELOPER.
NOW WE ADD THESE TWO MISTURES AND EQUATE THEM TO THE 11% MIXTURE OF 8+X PINTS
.11(8+X)
----------------------------------------------
.70*8+0X=.11(8+X)
5.6=.88+.11X
-.11X=.88-5.6
-.11X=-4.72
X=-4.72/-.11
X=42.9 PINTS OF WATER IS REQUIRED.
5.6=.11(8+42.9)
5.6=.11*50.9
5.6=5.6
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