<PRE><B>Question 1003650</B>
How much water must be mixed with 4 pints of a solution that is 90% developer to product a mixture that is 21% developer?
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Equation:
active + active = active
0.90*4 + 0*x = 0.21(4+x)
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90*4 + 0 = 21*4 + 21x
21x = 69*4
x = 13.1429 pints (amt. of water to add)
x = 13 1/7 pts
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Cheers,
Stan H.
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Options 
13 1/7 pt
13 1/3 pt 
16 20/21 pt 
17 1/7 pt </PRE>