## Evaluate Expressions - Evaluate expressions - Pre-Algebra Mathematics

A variable is a letter that represents unspecified numbers e.g. x, y or z.

6+x=12

To evaluate an algebraic expression you have to substitute each variable with a number and perform the operations included.

If we know the value of our variables we can substitute the variables for their values and thus evaluate the expression

Example

Calculate if x=3 and z=2

6z+4x=?

Replace x with 3 and z with 2 to evaluate the expression.

6z+4x=?

6x2+4x3=?

12+12=24

Video lesson: Evaluate the following expression for x = 2, y = 5 and z = 4

4x+(7-z)-6y

The solution can be seen in the video in the next page.

Here we have an algebraic equation rather than an expression that we want to evaluate for values of x, y and z and see what we get. The expression is 4x+(7-z)-6y. Now if we’re given values for x, z and y then we can evaluate this expression to some numerical value. We’re given x=2, z=4 and y=5. So here we have our values of x,z and y so we can just plug in our evaluate for those three values. So here we have four times two plus seven minus z is four and minus six times y which is five. Now we can just multiply these out and simplify a little bit from here. Four times two is eight, plus seven minus four is three. Minus six times five is thirty. Now we can add these, eight plus three is eleven minus thirty. Eleven minus thirty is negative nineteen.

John LewisUnited States of America -19??? Where did negative come from!!!2016-12-01 19:12:52

Patrice JacksonUnited States of America +11-30=-19; -30 is greater than +11, even if it was +30-11= 19 because 30 is greater than2016-12-05 15:12:40

Ahmed abd alkarimIreland how to add in the group please2016-09-08 22:09:34

Alan AndersonUnited Kingdom Do you mean the order of operations, Ahmed?2017-01-20 18:01:06

DeAnn CampbellUnited States of America This person does not follow order of operations. Rather confusing when the previous module was about Order of Operations.2016-06-19 19:06:15

Alan AndersonUnited Kingdom He does. This is the correct order of operations for this type of equation. The brackets and stuff are for more complex equations.2017-01-20 18:01:02

Toni WhitehouseUnited Kingdom none of them show topic completed2016-03-12 23:03:57

Siani GaelleCameroon We cant move to the next topic it says I have not done the Topic .2016-02-18 12:02:11

Alicia SanchezUnited States of America Nice and easy, but why cant I proceed to next Topic, and it says I haven't passed yet?2016-01-18 03:01:23

Alyssa DibiaaeUnited States of America Anyone notice that the text version say " minus 6 times y is 5" What!!!!!2015-12-17 03:12:33

anthony harmanAustralia Hi I'm new just started but we'reIis my math to do I watch the video then it says go to next topic so I do but it still says 0/1 completed on topic ?2015-10-20 16:10:14

Scott HappyUnited States of America Same problem, ever get it fixed?2015-11-12 11:11:48

Candance ShearnUnited States of America I have that same problem have you ever got the problem fixed.2015-11-03 09:11:15

Joyceadams SpencerUnited States of America Why was the answer a negative number?2015-09-16 11:09:06

Candance ShearnUnited States of America Because when you have 2 like numbers it is a positive and with not like numbers its negative.2015-11-03 10:11:54

Sharonae HillUnited States of America pretty simple2015-08-31 13:08:45

Joel PabuayaCanada High school all over2015-08-17 22:08:24