Question 280038
Ben nordstrom is developing film in his darkroom when he realizes he does not have the proper developer. He needs a mixture that is 20% developer, but he only has a mixture that is 90% developer. How much pure water must be mixed with 2 pints of 90% developer to produce the mixture he needs? 
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2 pints of 90% contains 1.8 pints of developer
That 1.8 pints is to be 20% in the new mix
--> the total = 9.0 pints
9 - 2 = 7 pints of water to be added