To conduct a scientific experiment, students need to mix 90mL of a 3% acid solution. They have a 1% and a 10% solution available. How many mL of the 1% solution and of the 10% solution should be combined to produce 90mL of the 3% solution?

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Answer 1 · 2015-10-15T01:41:19

You can do this with ratios.

The difference between 1% and 10% is 9.
You need to go up from 1% to 3% -- a difference of 2.

Then #2/9# of the stronger stuff has to be present, or in this case #20mL# (and of course #70mL# of the weaker stuff).