Substitution and evaluating expressions

Part 2

As mentioned earlier, plugging in variables is vital to math. In math, we call this substitution. We plug a number in for x to get a y. The best way to solve these quickly and easily is to plug in whatever number is given to you with parenthesis around it for x. For example, let's say we want to figure out how much money we will make from selling candy bars. This equation can be represented by y = 2x-7, where x equals the total amount of candy bars sold and y equals the total profit. If we sell 10 candy bars, we plug (10) in for x. So, we have equation 2(10)-7. The parenthesis means to multiply, so we do 2 times 10 to get 20, and then subtract 7 to get 13. So, our total profit is $13. It should be noticed that we have to do these problems in the order of PEMDAS, which was discussed in an earlier lesson.

The best way to get better at these is to practice. Try some here.

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