Intro to Evaluating Algebraic Expressions | How to Evaluate Algebraic Expressions | Math with Mr. J

welcome to math with Mr J [Music] in this video I'm going to cover how to evaluate expressions now to evaluate an expression that just means to find the value of the expression so what it equals once you work through it we will go through four examples two examples with one variable and two examples with two variables these examples will help us learn how to evaluate expressions using substitution they will set us up for Success moving forward and give us a strong Foundation to build off of once we start evaluating more complex Expressions let's jump into number one where we have X Plus 22. now for numbers one and two we need to evaluate these expressions or find the value of these Expressions when x equals five the first thing that we need to do we need to replace or plug in the given value for the variable that's called substitution so for number one let's plug five in for x and rewrite this expression so we have five Plus 22. now we can evaluate so we find out what this equals 5 plus 22 that equals 27. so the value of this expression is 27 when x equals 5. let's move on to number two where we have 8X now we have a number next to a variable that means we are multiplying so this is 8 times x let's plug in and evaluate so we have 8 times 5. eight times five equals 40. so the value of this expression is 40 when x equals 5. now one thing I do want to mention about number two when we plug 5 in for X make sure to use something to represent multiplication I used a DOT we can't put those two numbers together the eight and the five to represent multiplication that would look like 85 we can only put a number next to a variable to represent multiplication so something to keep in mind let's move on to numbers three and four where we have two variables and multiple operations we will start with number three where we have 7B minus a so 7 times B minus a let's start by plugging in the given values for A and B and we will rewrite this expression with those substitution ends so 7 times B well b equals nine so plug in 9 minus a a equals ten so plug in 10. now we can evaluate but we have more than one operation we have multiplication and subtraction so we need to use the order of operations PEMDAS in order to work through this so parentheses exponents multiplication and division then addition and subtraction multiplication comes before subtraction so let's multiply first seven times nine equals 63 then we can bring down the subtraction sign and the 10 we end with 63 minus 10 that equals 53. so the value of this expression is 53 when a equals 10 and b equals 9. lastly let's move on to number four where we have a plus 18 divided by B let's plug in and evaluate a equals 10 so plug in 10 for a plus 18 divided by b b equals nine so plug in 9 for B we have addition and division so we need to go through the Order of Operations Division comes before addition so let's divide first 18 divided by 9 equals 2. bring down the addition sign and the 10. so we end with 10 plus two ten plus two equals 12. so the value of this expression is 12 when a equals 10 and b equals 9. so there you have it there's an introduction to evaluating expressions using substitution I dropped links to more videos and examples down in the description those are great follow-ups to this introduction I hope that helped thanks so much for watching until next time peace