Alligation / Ratio Question

by Michelle

I completed the following problem using the tic tac toe alligation chart, but my answers don't match the answer key. The problem is:

Rx: Prepare 480 mL of a 1:30 solution using a 1:10 solution and a 1:50 solution. What quantities will be used of each stock solution to make the 1:30 solution?

To compute this, I converted the ratios to percentages and used the tic tac toe chart. As a result I got 60 ml for the 10 % solution and 420 ml for the 2% solution. These quantities add up to 480, so I thought I had done the problem right, however the answer is listed as : 78 mL of 1:10, 402 mL of 1:50.

I cannot figure out how they got this answer. Are there steps I need to take beyond the basic alligation chart? Do the ratios change the problem from the basic alligation problem? I'm so confused.

Click here to post comments.

Join in and write your own page! It's easy to do. How?
Simply click here to return to Ask a Math Question