Question 1175881
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You should know and understand the formal algebraic method for solving 2-part mixture problems like this, as shown by the other tutor.<br>
If a formal algebraic solution is not required, and if solving the problem as fast as possible is desired (as in a timed mathematics competition) here is a quick and easy way of solving any problem like this.<br>
You are starting with a 9% solution and adding 3% solution to end up with a 5% solution.<br>
Think of the problem like this:
(1) I'm starting at 9% and heading towards 3%, stopping when I get to 5%.
(2) 5% is 2/3 of the way from 9% to 3%. (picture the three percentages on a number line....)
(3) That means 2/3 of the mixture is the 3% solution that I am adding.<br>
So the 10mL of 9% you started with is 1/3 of the final solution; that means the 2/3 you added is 20mL.<br>
ANSWER: 20mL<br>
CHECK:
.09(10)+.03(20) = .9+.6 = 1.5
.05(10+20) = .05(30) = 1.5<br>