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.

Barbara Eastwood-waltersUnited States of America These examples are great but when I finish the section it will not go onto the next. I have clicked on finish several times and it will not go forward.2015-06-24 16:06:42

SANDRA MOSSUnited States of America great2015-02-24 15:02:02

Karin RootsUnited States of America Okay so if .....4(2)+(7-4)-6(5) = 8+(3)-30 8+3=11-30......THEREFORE, THE ANSWER IS :19........SO BASICALLY SUPPLEMENT BOTH THE LETTERS AND NUMBERS INTO THEIR CORRECT PLACE(VALUES) AND LASTLY ....CONTINUE TO WORK THROUGH THE EQUATION UNTIL THE ANSWER HAS BEEN SOLVED.2015-02-22 23:02:42

Michelle THEODOREPapua New Guinea Could you please do the solving for this work.Thank you2015-05-12 00:05:36

Brandy TreibUnited States of America "Finish" button doesn't work, have to exit course and begin next module without any credit shown.2015-01-22 02:01:04

Tonya SpencerUnited States of America Sorry i meant to say page2015-01-14 03:01:12

Tonya SpencerUnited States of America something is wrong with this age . No test or anything2015-01-14 03:01:11

Bernard VerdamCanada i seem to be in a loop. there is no test / eval, and the modules that i viewed show as incomplete2014-12-16 20:12:58

Kamryn PreeceUnited States of America you have to click finish the course for it to show as completed...2015-01-05 19:01:20

Jo BaileyUnited Kingdom how does this course system work?2014-08-12 16:08:13

Tia Joseph Mzz LovelessTrinidad and Tobago am on expressions and i took a book and a pen and its pretty easier that way when i work with them2014-08-15 01:08:19