On the first question, it says my answer is wrong and I got 18 as my answer.

At first i got that too, but then i realized there was a -6 at the end of the problem. So the actual answer was 12. :)

i dont get the 2nd q how do we solve it when its an fraction

a fraction is division. so 10 divided by 5 can be written as a fraction 10/5, and x/y means x divided by y. does that help? you would do it along with multiplication in the order of operations.

how do you expand and simplify: 2(x- 1)(x+1)+(2x-1)(2x-1)

First distribute 3x over (2x+5) and then distribute -2x over (x-6): 3x(2x+5) - 2x(x-6) = 6x^2 + 15x - 2x^2 + 12x [Note: -2x * -6 = +12x, not -12x] = 6x^2 - 2x^2 + 15x + 12x [Rewrite with like terms in order.] = 4x^2 + 27x

how can i find the answer in the equation 5x - x/y when x=4 and y =2

1) Substitute each value into the expression for their respective variable `5(4) - 4/2` 2) Follow PEMDAS -- Multiply: `20 - 4/2` -- Divide: `20 - 2` -- Subtract: `18` Hope this helps.

Assuming you are asking about the 1st practice exercise... If you got an answer of 18, you ignored the -6 on the right side. 6(1)+4(3-6 = 6+12-6 = 18-6 = 12 Hope this helps.

How come when evaluating expressions with two variables (the previous section) that the minus was completed prior to the plus. The questions was xy - y + 3x where x = 3 and y =2. BOMDAS 3 x 2 - 2 + 3 x 3 = 6 - 2 + 9 6 - 11

xy-y+3x , if x=3 and y=2 results to 6 - 2 + 9 = 13. Either a parenthesis in the exercise got lost or the solution is wrong, but for the given expression the above result is the correct solution.

does the BODMAS order of operations apply here? because i tried doing these exercises by applying addition before subtraction and it gives a different answer

BODMAS applies when evaluating / simplifying all expressions. But, you are making a common mistake. People use the acronym too literally. There are 4 steps, not 6. B = Brackets or Parentheses: Do all work inside parentheses / grouping symbols O = Orders or Exponents & radicals DM = Divide & Multiple from left to right. This is one rule/step. It is not divide then multiple. Which every is on the left gets done 1st. AS = Add & Subtract from left to right. Again, this is one rule/step. It is not add then subtract. Which every operation is on the left gets done first. If the subtraction is on the left in the problem, then it comes before the addition. Hope this helps.

Main content

Algebra 1

Course: Algebra 1 > Unit 1

Lesson 3: Substitution and evaluating expressions

Evaluating expressions with two variables

Google Classroom

We've already evaluated expressions with one variable. Now it's time to do it with two variables.

Khan Academy video wrapper

Evaluating expressions with two variablesSee video transcript

How to evaluate an expression with two variables

Let's say we want to evaluate the expression

10 + 2 p - 3 r

. Well, first we need to know the values of

p

and

r

. For example, to evaluate the expression when

p = 4

and

r = 5

, we just replace

p

with

4

and

r

with

5

$10 + 2 p - 3 r$ ‍

$= 10 + 2 \cdot 4 - 3 \cdot 5$ ‍

$= 10 + 8 - 15$ ‍

$= 3$ ‍

So, the expression

10 + 2 p - 3 r

equals

3

when

p = 4

and

r = 5

Now, let's practice

Problem 1

Evaluate $6 a + 4 b - 6$ ‍ when $a = 1$ ‍ and $b = 3$ ‍.

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hrhsimonn
Posted 7 years ago. Direct link to hrhsimonn's post “On the first question, it...”
On the first question, it says my answer is wrong and I got 18 as my answer.
Button navigates to signup pageComment on hrhsimonn's post “On the first question, it...”
(74 votes)
Answer
- Ryenn Smith
  Posted 4 years ago. Direct link to Ryenn Smith's post “At first i got that too, ...”
  At first i got that too, but then i realized there was a -6 at the end of the problem. So the actual answer was 12. :)
  Comment on Ryenn Smith's post “At first i got that too, ...”
  (102 votes)
Xinyi Ni
Posted 4 years ago. Direct link to Xinyi Ni's post “i dont get the 2nd q how ...”
i dont get the 2nd q how do we solve it when its an fraction
Button navigates to signup pageComment on Xinyi Ni's post “i dont get the 2nd q how ...”
(18 votes)
Answer
- loumast17
  Posted 4 years ago. Direct link to loumast17's post “a fraction is division. ...”
  a fraction is division. so 10 divided by 5 can be written as a fraction 10/5, and x/y means x divided by y. does that help? you would do it along with multiplication in the order of operations.
  Comment on loumast17's post “a fraction is division. ...”
  (34 votes)
Ayesha Griffith
Posted 7 years ago. Direct link to Ayesha Griffith's post “how do you expand and sim...”
how do you expand and simplify: 2(x- 1)(x+1)+(2x-1)(2x-1)
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(12 votes)
Answer
- live2tutor
  Posted 7 years ago. Direct link to live2tutor's post “First distribute 3x over ...”
  First distribute 3x over (2x+5) and then distribute -2x over (x-6):
  3x(2x+5) - 2x(x-6)
  = 6x^2 + 15x - 2x^2 + 12x [Note: -2x * -6 = +12x, not -12x]
  = 6x^2 - 2x^2 + 15x + 12x [Rewrite with like terms in order.]
  = 4x^2 + 27x
  Comment on live2tutor's post “First distribute 3x over ...”
  (21 votes)
devarshrana3
Posted 5 months ago. Direct link to devarshrana3's post “easy peasy lemon squezy”
easy peasy lemon squezy
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(19 votes)
Answer
- Mason Tagalogon
  Posted 2 months ago. Direct link to Mason Tagalogon's post “how is your day going”
  how is your day going
  Comment on Mason Tagalogon's post “how is your day going”
  (3 votes)
Bookworm
Posted 6 years ago. Direct link to Bookworm's post “how can i find the answer...”
how can i find the answer in the equation 5x - x/y when x=4 and y =2
Button navigates to signup pageComment on Bookworm's post “how can i find the answer...”
(9 votes)
Answer
- Kim Seidel
  Posted 6 years ago. Direct link to Kim Seidel's post “1) Substitute each value...”
  1) Substitute each value into the expression for their respective variable
  5(4) - 4/2
  2) Follow PEMDAS
  -- Multiply: 20 - 4/2
  -- Divide: 20 - 2
  -- Subtract: 18
  Hope this helps.
  Comment on Kim Seidel's post “1) Substitute each value...”
  (17 votes)
alyssa.allen
Posted 4 months ago. Direct link to alyssa.allen's post “how is it not 18”
how is it not 18
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(7 votes)
Answer
- Kim Seidel
  Posted 4 months ago. Direct link to Kim Seidel's post “Assuming you are asking a...”
  Assuming you are asking about the 1st practice exercise... If you got an answer of 18, you ignored the -6 on the right side.
  6(1)+4(3-6 = 6+12-6 = 18-6 = 12
  
  Hope this helps.
  Comment on Kim Seidel's post “Assuming you are asking a...”
  (13 votes)
352789341
Posted 7 months ago. Direct link to 352789341's post “are we always gonna be sh...”
are we always gonna be shown the numbers the variables represent when doing the work?
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(9 votes)
Answer
- Kim Seidel
  Posted 7 months ago. Direct link to Kim Seidel's post “With these types of probl...”
  With these types of problems, yes you would be given the values to use.
  
  You will also learn how to simplify the expressions (where values are not given), and that becomes the basis for learning how to solve algebraic equations where you can solve to find the value for the variable.
  Button navigates to signup page
  (1 vote)
Viki Morgan
Posted 8 years ago. Direct link to Viki Morgan's post “How come when evaluating ...”
How come when evaluating expressions with two variables (the previous section) that the minus was completed prior to the plus. The questions was xy - y + 3x where x = 3 and y =2. BOMDAS 3 x 2 - 2 + 3 x 3 =
6 - 2 + 9
6 - 11
Button navigates to signup pageComment on Viki Morgan's post “How come when evaluating ...”
(5 votes)
Answer
- dashpointdash
  Posted 8 years ago. Direct link to dashpointdash's post “xy-y+3x , if x=3 and y=2 ...”
  xy-y+3x , if x=3 and y=2 results to 6 - 2 + 9 = 13.
  
  Either a parenthesis in the exercise got lost or the solution is wrong,
  but for the given expression the above result is the correct solution.
  Comment on dashpointdash's post “xy-y+3x , if x=3 and y=2 ...”
  (13 votes)
Billy Wells
Posted 4 years ago. Direct link to Billy Wells's post “After coming back from th...”
After coming back from the Holiday BELIEVE ME! I had to go through these problems more than (2)- (3) times. Knowing how much I love math this, probably was one of the toughest days ever. This is how I solved the First and second problems:

10+2p-3k ( p=4, r=5)
10 +2*4-3*5
10+8-15
18-15=3

6a+4b-6 ( a=1, b=3)
6*1+4*3-6
6+12-6
18-6=12
Button navigates to signup pageComment on Billy Wells's post “After coming back from th...”
(11 votes)
Answer
- nahnahihalima09
  Posted 9 months ago. Direct link to nahnahihalima09's post “That is correct! Great jo...”
  That is correct! Great job!
  Button navigates to signup page
  (0 votes)
SulayxGalma
Posted 6 months ago. Direct link to SulayxGalma's post “does the BODMAS order of ...”
does the BODMAS order of operations apply here? because i tried doing these exercises by applying addition before subtraction and it gives a different answer
Button navigates to signup pageButton navigates to signup page
(3 votes)
Answer
- Kim Seidel
  Posted 6 months ago. Direct link to Kim Seidel's post “BODMAS applies when evalu...”
  BODMAS applies when evaluating / simplifying all expressions. But, you are making a common mistake. People use the acronym too literally. There are 4 steps, not 6.
  
  B = Brackets or Parentheses: Do all work inside parentheses / grouping symbols
  
  O = Orders or Exponents & radicals
  
  DM = Divide & Multiple from left to right. This is one rule/step. It is not divide then multiple. Which every is on the left gets done 1st.
  
  AS = Add & Subtract from left to right. Again, this is one rule/step. It is not add then subtract. Which every operation is on the left gets done first. If the subtraction is on the left in the problem, then it comes before the addition.
  
  Hope this helps.
  Comment on Kim Seidel's post “BODMAS applies when evalu...”
  (14 votes)