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Percent Concentrations - Concept
MA, Stanford University
Teaching in the San Francisco Bay Area
Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts
To solve word problems involving percent concentration amounts, knowledge of solving systems of equations and percents is necessary. Percent concentration word problems involve solving for amounts and concentrations when mixing two liquids with differing percent concentration amounts. Other types of word problems using systems of equations include mixture problems and money word problems.
Percent concentration word problems can be really mind boggling when you look at them. Because it's going to look like 20 percent alcohol is combined with 5 milliliters of 30 percent alcohol to get a result, I mean it has lots and lots of fancy language. It's going to use the word percent, the word concentration, you're going to have to deal with milliliters probably or some kind of measurement for liquid. Just you guys when you come to these problems slow down, take your time read it carefully and remember this formula I'm showing you here. You're going to take the amount, times and concentration of your first ingredient I'm abbreviating amount by the way to amt plus the amount times the concentration of your second ingredient and that's going to equal your mixture amount times your mixture concentration.
If you can keep that straight in your head and just go slowly when you read the problem, you're going to be in good shape. One other thing I want remind you of whey you're doing thiese problems is how to work with decimals and percents. Something like 28 percent you're probably going to write it as 0.28 you could also write it as 28 one hundreds if you were like a fractions superstar, you don't have to. Most people chose to use this as 0.28 so that they can do these problems on their calculator. You don't have to use the fractions and if you try to use the percent sign you're going to run into trouble when you try to type it into your calculator. So make sure you're converting from the percent number to its decimal representation.
One other thing that gets tricky with that, is if you have 8 percent remember that means point 0.08 don't write 0.8 because that is 80 percent. You'll know that when you see it. Alright guys good luck on these problems use this formula and read carefully.
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Sample Problems (4)
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Problem 1 4,791 views
How many mL of a 50% alcohol solution must be mixed with 1 mL of a 10% alcohol solution to get a 46% alcohol solution?
Problem 2 3,493 views
For a graduation party, Amelia mixed 9 gallons of brand A lemonade with 6 gallons of brand B lemonade. Brand A contains 28% real fruit juice and brand B contains 18% real fruit juice.What percent of the mixture is real fruit juice?
Problem 3 3,012 views
Rudy wants to make a 21% sugar solution. He has already poured 1 fl. oz. of pure water into a beaker.How many fl. oz. of a 28% sugar solution must he add to this to create the desired mixture?
Problem 4 126 views