7) 80% cleansing powder = 20% water = .20 60% cleansing powder = 40% water = .40 pure water = 100% = 1
This one is a little trickier......I hope I've done it correctly....!!!
Let's call the amount we draw off = x And this is = to the amount of pure water we replace it with....so we have....
.20water * [ starting amount - amt drawn off] plus "x" amt of pure water = 40% water * 200L
.20(200-x) + 1x = .40 [ 200] simplify
40 - .20x + 1x = 80
40 + .80x = 80 subtract 40 from each side
.80x = 40 divide both sides by ..80
x = 40/.80 = 50 mL = amt drawn off
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