For the second expression, 3(2)-2+3(3)= 5 not 13 I thought you were suppose to add before you subtract?

(1.) 3(2) - 2 + 3(3) (Multiply 3 by 2 and 3 by 3 because multiplication comes before addition or subtraction.) (2.) 6 - 2 + 9 (Because we move from left to right, we subtract first.) (3.) 4 + 9 = 13

I thought PEMDAS is applied to Algebra? The last example that Sal gave made me confused. Can someone help me?

MD (Multiplication and Division) and AS (Addition and Subtraction) go left to right. If a division problem comes before a multiplication problem, you do the division first.

What does it mean when numbers are in parentheses?

That means that you simply need to do the math inside those parentheses first. Example: 2 + 3 * 5 = 2 + 15 = 17 (2 + 3) * 5 = 6 * 5 = 30

When the equation comes to "6 - 2 + 9" would the answer not be minus 5? should you not add 9 and 2 and then subtract because of the order of operations ?

This can be a common misunderstanding of the "order of operations" if you are using a mnemonic to remember them by. Multiplication and Division happen at the same time, not multiply first, then divide, and the same for addition and subtraction. You don't do all the adding and then do all the subtraction, you do them at once (unless there are brackets/parenthesis of course). So in this case, it is 6 plus -2 plus 9 and you can put those in any order too 9 plus 6 plus -2 / -2 plus 9 plus 6 / -2 plus 6 plus 9 etc.

I'm so confused. HOW are you deciding what numbers each of the letters are? How are you deciding the a=7, b=2, x=3 and y=2?

ye hannah's right for random problems you can come up with random variables, the problems that people are determining true real life stuff like a rockets fins, you actually need to be precise.

can i write the dot which represent (x)times on any topic

Yes, it is just another way of showing multiplication.

So do we do BEDMAS to work out the answer or just the order of expressions?

PEMDAS is only used to work out the order of operations, or which expressions to calculate first.

Say X is 45 and Y is 5 what would you get X+Y?

Plug in the values and you'll get 45 + 5 which is 50.

when he said a=7 and b=2 how did hecome up with that all his own and also y=2 and x=3 how is those correct ?

Sometimes you will be told what value the variables will have, like this: X + 3 = 5. Solve for X. Well, what number could X possibly be? As you learned, 2 + 3 = 5 so X must equal 2. But sometimes, you will be told what value the variable has and you are asked to solve the problem: If X = 5, solve this equation: X + 3 - 2 + X. Here you simply change all of the X's to 5's and solve the problem. So it becomes 5 + 3 - 2 + 5. Which equals 11. Since this is an introduction to expressions with more than one variable, he's simply making them up so he can show you some examples.

Main content

Algebra (all content)

Course: Algebra (all content) > Unit 1

Lesson 3: Substitution and evaluating expressions

Evaluating expressions with two variables

Name: Evaluating expressions with two variables
Uploaded: 2013-10-26T00:20:42Z
Description: We've done a few examples together where we were faced with 1 variable. Why not try one that has 2 variables?

CCSS.Math:

6.EE.A.2

6.EE.A.2c

Google Classroom

We've done a few examples together where we were faced with 1 variable. Why not try one that has 2 variables? Created by Sal Khan.

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Angie Britton
Posted 5 years ago. Direct link to Angie Britton's post “For the second expression...”
For the second expression, 3(2)-2+3(3)= 5 not 13
I thought you were suppose to add before you subtract?
Button navigates to signup pageComment on Angie Britton's post “For the second expression...”
(39 votes)
Answer
- Anthony Fritz
  Posted 5 years ago. Direct link to Anthony Fritz's post “(1.) 3(2) - 2 + 3(3) (Mul...”
  (1.) 3(2) - 2 + 3(3) (Multiply 3 by 2 and 3 by 3 because multiplication comes before addition or subtraction.)
  (2.) 6 - 2 + 9 (Because we move from left to right, we subtract first.)
  (3.) 4 + 9 = 13
  Button navigates to signup page
  (4 votes)
Elhison Raphael B. Cortez
Posted 5 years ago. Direct link to Elhison Raphael B. Cortez's post “I thought PEMDAS is appli...”
I thought PEMDAS is applied to Algebra? The last example that Sal gave made me confused. Can someone help me?
Button navigates to signup pageComment on Elhison Raphael B. Cortez's post “I thought PEMDAS is appli...”
(26 votes)
Answer
- Jack Kaczmarski
  Posted 3 years ago. Direct link to Jack Kaczmarski's post “MD (Multiplication and Di...”
  MD (Multiplication and Division) and AS (Addition and Subtraction) go left to right. If a division problem comes before a multiplication problem, you do the division first.
  Button navigates to signup page
  (15 votes)
supergirl78.dg
Posted 4 years ago. Direct link to supergirl78.dg's post “What does it mean when nu...”
What does it mean when numbers are in parentheses?
Button navigates to signup pageComment on supergirl78.dg's post “What does it mean when nu...”
(14 votes)
Answer
- eddiemin
  Posted 4 years ago. Direct link to eddiemin's post “That means that you simpl...”
  That means that you simply need to do the math inside those parentheses first.
  
  Example:
  
  2 + 3 * 5 = 2 + 15 = 17
  (2 + 3) * 5 = 6 * 5 = 30
  Comment on eddiemin's post “That means that you simpl...”
  (14 votes)
Clodagh Burke
Posted 6 years ago. Direct link to Clodagh Burke's post “When the equation comes t...”
When the equation comes to "6 - 2 + 9" would the answer not be minus 5? should you not add 9 and 2 and then subtract because of the order of operations ?
Comment on Clodagh Burke's post “When the equation comes t...”
(9 votes)
- Chris Nolan.ca
  Posted 6 years ago. Direct link to Chris Nolan.ca's post “This can be a common misu...”
  This can be a common misunderstanding of the "order of operations" if you are using a mnemonic to remember them by. Multiplication and Division happen at the same time, not multiply first, then divide, and the same for addition and subtraction. You don't do all the adding and then do all the subtraction, you do them at once (unless there are brackets/parenthesis of course).
  
  So in this case, it is
  6 plus -2 plus 9 and you can put those in any order too
  9 plus 6 plus -2 / -2 plus 9 plus 6 / -2 plus 6 plus 9 etc.
  Comment on Chris Nolan.ca's post “This can be a common misu...”
  (16 votes)
DANIEL
Posted 5 years ago. Direct link to DANIEL's post “can i write the dot which...”
can i write the dot which represent (x)times on any topic
Button navigates to signup pageComment on DANIEL's post “can i write the dot which...”
(7 votes)
Answer
- captain wolf
  Posted 3 years ago. Direct link to captain wolf's post “Yes, it is just another w...”
  Yes, it is just another way of showing multiplication.
  Button navigates to signup page
  (6 votes)
Vladimir
Posted 2 years ago. Direct link to Vladimir's post “I'm so confused. HOW are ...”
I'm so confused. HOW are you deciding what numbers each of the letters are? How are you deciding the a=7, b=2, x=3 and y=2?
Button navigates to signup pageComment on Vladimir's post “I'm so confused. HOW are ...”
(9 votes)
Answer
- Blake Meloche (T1)
  Posted 2 months ago. Direct link to Blake Meloche (T1)'s post “ye hannah's right for ran...”
  ye hannah's right for random problems you can come up with random variables, the problems that people are determining true real life stuff like a rockets fins, you actually need to be precise.
  Button navigates to signup page
  (2 votes)
freya
Posted 5 years ago. Direct link to freya's post “So do we do BEDMAS to wor...”
So do we do BEDMAS to work out the answer or just the order of expressions?
Button navigates to signup pageComment on freya's post “So do we do BEDMAS to wor...”
(6 votes)
Answer
- Lexi Adams
  Posted 5 years ago. Direct link to Lexi Adams's post “PEMDAS is only used to wo...”
  PEMDAS is only used to work out the order of operations, or which expressions to calculate first.
  Comment on Lexi Adams's post “PEMDAS is only used to wo...”
  (7 votes)
Brian
Posted 2 years ago. Direct link to Brian's post “Say X is 45 and Y is 5 wh...”
Say X is 45 and Y is 5 what would you get X+Y?
Button navigates to signup pageComment on Brian's post “Say X is 45 and Y is 5 wh...”
(4 votes)
Answer
- Jeremiah
  Posted 5 months ago. Direct link to Jeremiah's post “Plug in the values and yo...”
  Plug in the values and you'll get 45 + 5 which is 50.
  Button navigates to signup page
  (4 votes)
jlmartinez23
Posted 5 years ago. Direct link to jlmartinez23's post “i wonder how we could slo...”
i wonder how we could slove math fater and earier
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(6 votes)
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- MM PLAYS
  Posted 10 days ago. Direct link to MM PLAYS's post “You can keep practicing a...”
  You can keep practicing and get help from people!! :D
  Button navigates to signup page
  (1 vote)
RicAlcaraz96
Posted 7 years ago. Direct link to RicAlcaraz96's post “when he said a=7 and b=2 ...”
when he said a=7 and b=2 how did hecome up with that all his own and also y=2 and x=3 how is those correct ?
Button navigates to signup pageComment on RicAlcaraz96's post “when he said a=7 and b=2 ...”
(3 votes)
Answer
- KathyC
  Posted 7 years ago. Direct link to KathyC's post “Sometimes you will be tol...”
  Sometimes you will be told what value the variables will have, like this:
  X + 3 = 5. Solve for X. Well, what number could X possibly be? As you learned, 2 + 3 = 5 so X must equal 2.
  
  But sometimes, you will be told what value the variable has and you are asked to solve the problem:
  If X = 5, solve this equation: X + 3 - 2 + X. Here you simply change all of the X's to 5's and solve the problem. So it becomes 5 + 3 - 2 + 5. Which equals 11.
  
  Since this is an introduction to expressions with more than one variable, he's simply making them up so he can show you some examples.
  Comment on KathyC's post “Sometimes you will be tol...”
  (2 votes)

Video transcript

Now, let's think about expressions with more than one variable. So say I had the expression a plus-- I'll do a really simple one, a plus b. And I want to evaluate this expression when a is equal to 7 and b is equal to 2. And I encourage you to pause this and try this on your own. Well, wherever we see the a, we would just replace it with the 7. And wherever we see the b, we'd replace it with the 2. So when a equals 7 and b equals 2, this expression will be 7 plus 2, which, of course, is equal to 9. So this expression would be equal to 9 in this circumstance. Let's do a slightly more complicated one. Let's say we have the expression x times y minus y plus x. Actually, let's make it plus 3x. Or another way of saying it plus 3 times x. So let's evaluate this when x is equal to 3 and y is equal to 2. And once again, I encourage you to pause this video and try this on your own. Well, everywhere we see an x, let's replace it with a 3. Every place we see a y, let's replace it with a 2. So this is going to be equal to 3 times y. And y is 2 in this case. 3 times 2 minus 2 plus this 3 times x. But x is also now equal to 3. So what is this going to be equal to? Well, this is going to be equal to 3 times 2 is 6. This 3 times 3 is 9. So it simplifies to 6 minus 2, which is 4, plus 9, which is equal to 13. So in this case, it is equal to 13.