Substitution and evaluating expressions

Part 1

Sometimes you will know what number a variable represents, and in these situations, you can plug in whatever x is supposed to represent into the equation. For example, if you are trying to calculate how many people can fit on a school bus, a common equation would be 2x + 1. X represents the amount of those weird seats on the school bus. So, if we know that we have 8 seats on our school bus, we know that we can hold 17 people. All you have to do is plug 8 in for x. Remember, that x is multiplied by the coefficient. So, we can multiply 8 by 2 and then add 1 to get 17. Use PEMDAS listed in other questions to solve the problem. However, one thing you need to remember is that coefficients are multiplication, so you need to solve them at the multiplication step.

When solving 3(5x-2) when x = 5, we first do the things in the parenthesis. The first step that comes up in PEMDAS that is applicable after parenthesis is multiplication, so we plug 5 into x and multiply 5 and 5 to get 25. Then, we finish the parenthesis by subtracting 2 from 25 to get 23.

The best way to evaluate these types of problems is with practice. Try some of the examples below.

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