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You can put this solution on YOUR website!
\n" ); document.write( "The problem is presented as a drain and replace problem just to confuse you. What you really have is just a mixture problem where you want to mix 20% antifreeze with 100% antifreeze to get 70 liters of 40% antifreeze.
\n" ); document.write( "There are many ways of solving problems like this where you are mixing two ingredients. The response from the other tutor shows a typical algebraic method.
\n" ); document.write( "In my opinion, there is a much easier and faster way to solve this kind of problem, using the ratio in which the two ingredients need to be mixed.
\n" ); document.write( "For this problem, we are mixing 20% and 100% antifreeze ingredients to get a 40% antifreeze mixture. The ratio in which the ingredients must be mixed is directly related to where the 40% lies between the 20% and the 100%.
\n" ); document.write( "To be short with the explanation, 40% is 1/4 of the way from 20% to 100%. (20% to 40% is 20%; 20% to 100% is 80%; 20% is 1/4 of 80%.) That means 1/4 of the mixture must be the 100% ingredient.
\n" ); document.write( "So 1/4 of the 70 liters, or 17.5 liters, is the 100% antifreeze that you added; the remaining 3/4 of the 70 liters, or 52.5 liters, is the 20% antifreeze that was already in the radiator.
\n" ); document.write( "To put that result in the terms in which the question was asked, 17.5 liters of the 20% antifreeze must be drained and replaced with 100% antifreeze to get 70 liters of 40% antifreeze.
\n" ); document.write( "So in the end here is all that is required to solve this problem:
\n" ); document.write( "40-20 = 20; 100-20 = 80; 20/80 = 1/4; 1/4 of 70 = 17.5
\n" ); document.write( "If your mental arithmetic is good, it will take you about 10 seconds to work the problem. \n" ); document.write( "