## 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.

joseph lasaroPapua New Guinea what is the sing of the point?2017-03-20 00:03:41

Edith NgugiKenya best when we summarize by saying we work all with the mnemonic BODMAS.(brackets ,of,division,multiplication ,addition and subtraction)workin from left to right2017-02-23 13:02:51

Natalee WellingtonJamaica can i get some help please i am unable to see the content of the topic it is saying a plug in is needed to display.. can someone please tell me what type of plugin.2017-01-27 16:01:37

Christopher BeckerSouth Africa Wich Operating system and browser are you using Natalee? At the top right hand corner of your browser you should be able to drop down th menu button. Go to >estensions >search for more extensions >type 'flash players' and download the flash player extension.2017-01-30 08:01:02

Anamaria Cristina TusaNetherlands guys i know how to start the next topic. so, after u finish the currently topic, press 'exit course' thn press 'finish' , nd ur module is completed! c.ya!!!2017-01-26 21:01:23

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

Anamaria Cristina TusaNetherlands well... minus with minus = + plus with plus=+ minus with plus=-(minus) plus with minus=-(minus)2017-01-26 21:01:15

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

Anamaria Cristina TusaNetherlands right. idk wht to do either :)))2017-01-26 21:01:27

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

Anamaria Cristina TusaNetherlands y identify 5. y is number 5. So ...you calculate ......-6x5= :)2017-01-26 21:01:13