<p>20 grams of solution A has 10% alcohol by mass and 15 grams of solution B has 20% alcohol by mass. If 10 grams of Solution A is added to 10 grams of Solution B, what is the percent alcohol in this mixture? </p>
<p>Free response.</p>
<p>20 grams of solution A has 2 grams of alcohol. 15 grams of solution B has 3 grams of alcohol. That must mean 10 grams of solution A has 1 gram of alcohol, and 10 grams of solution B has 2 grams of alcohol. Then, you add them together. So, the answer is 3/20 or 15%. If I’m wrong, sorry about that and please correct me. Thanks :)</p>
<p>Is 12.5 right?</p>
<p>((10g A * .10)+(10g B * .15))/20 * 100</p>
<p>EDIT: Whoops, misread.</p>
<p>((10g A * .10)+(10g B * .20))/20 * 100</p>
<p>15%</p>
<p>I just assumed the percent of alcohol doesn’t change since they’re both solutions.</p>
<p>The quantities mentioned initially, 20 g of Solution A and 15 g of Solution B, are extraneous information. They’re just added to confuse you.</p>
<p>If Solution A is 10% alcohol by mass, then the 10 g that will be combined with B contains 1 g of alcohol. Similarly, if Solution B is 20% alcohol by mass, then the 10 g that will be combined with Solution A contains 2 g of alcohol.</p>
<p>That makes, as Yakisoba said, 3 g of alcohol, out of a solution that has 20 g total mass. And 3/20 is indeed 15%.</p>
<p>Yakisoba’s solution–er, answer–is correct. (And now that I’ve reread ybrown’s more closely–and I see that “10g” is “ten grams,” and not “logarithm,” as I had first thought–I see that ybrown is also correct.)</p>
<p>Haha, “solution”</p>
<p>And I could’ve sworn I responded to somebody’s comment that was between my two posts o.o</p>
<p>I thought there was another post in there, too, ybrown! User must’ve deleted it while it was still available to edit.</p>
<p>@ybrown234 yeah, I saw your answer was different from mine, so I asked to see if I did anything wrong, but then I saw that you changed your answer. :)</p>