Question 1095106
<br>I will assume you will get at least one response that show the traditional algebraic method for solving this kind of problem; I will just show you my quick shortcut method....<br>
The 7% that she wants is "twice as close" to the 9% that is being added as it is to the 3% she is starting with.  That is, 9-7 = 2; while 7-3=4; 7 is "twice as close to 9 as it is to 3".<br>
Since the percentage of the mixture is twice as close to 9% as it is to 3%, she needs twice as much of the 9% as she has of the 3%.  Since she has 60ml of the 3%, she needs 120ml of the 9%.<br>
Answer: 120 ml