How to evaluate expressions with two variables | 6th grade | Khan Academy

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

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I CAN NEVER THANK YOU ENOUGH!! I had a math test about this but my teacher explained it hard so i was confused but i saw this video and i get it now! I GOT AN 8/8 ON MY TEST TYSM

niyoka
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Thank you Khanacademy. You are the best!

rubymendez
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Funny watching this at 21 years old... I'm wanting to become an electrician and they require knowledge of basic Algebra 1... I don't remember any of this stuff as I was pretty hard headed in math.

Kenworth
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Could you please explain why you are not following the PEMDAS rules?
I am also trying to do these on the Khan Academy website and I keep getting the answers wrong because I've only known to use PEMDAS.
I thought it should be; 6-2+9 > 6-11 > Answer being -5.

Thanks in advance for your response!

aaronmac
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The order of operations is what is important! This reminds me of the Ma and Pa Kettle of Math video!

TheFalconJetDriver
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Isn't the 2nd answer supposed to be 5? PEMDAS says addition first before subtraction, so why don't we add 2+9 instead of 6-2 ???

madmaddox
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I'm doing good at learning so far :)

papangack
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11강 : Algebra 1 - Unit1 - lesson 3 -1/2
L3 Substitution and evaluating expressions
1/2 Evaluating expressions with two variables

1. Now, let's think about expressions with more than one variable. 0:01
2. 0:03 I'll 0:08
So say I had the expression a plus-- a plus, I'll do a really simple one, a plus b.
아주 간단한 식 a+b를 해보겠습니다.
3. 0:11
And I want to evaluate this expression when a is equal to 7 and b is equal to 2.
애나워느 밸류에잇 디스익스프레션
a=7, b=2일 때 식을 구해보려 합니다.

4. 0:20
Encourage you to pause this and try this on your own.
엔커리지 유르 파지스 트라이 디스 온유어온
먼저 영상을 멈추고 스스로 풀어보시길 권장합니다.

5. 0:22 0:24
Well we, wherever we see the a, we would just replace it with the 7.
웰위, 웨얼버위 씨디에이, 위저슷 리플레이싯 윗드 더쎄븐
a가 있는 모든 자리에 7을 대입하고
6. 0:26 0:28
And wherever we see, we see the b, / we'd replace it with the 2.
앤 웨얼버위어 씨, 우이 씨더비, 위드 리플레이싯 윗더투
b에는 모두 2를 대입해줍니다.

7. 0:30
8. 0:38 0:40
9. 0:42
10. 0:45
Let's say we have the expression x times y minus y plus x.

11. 0:57
Actually, let's make it plus 3x.
액츄 렛스메이킷 플러스 뜨리엑스
잠깐 3x로 고치겠습니다
12. 1:00 1:01
Or another way of saying it plus 3 times x.
3x는 다시 말해 3×x이죠
13. 1:05
14. 1:15
15. 1:19 let's 1:20 / 1:21 1:22 1:23
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.
웰 에브리웨얼우이 씨언 엑스, (렛스)리플레이싯 윗더뜨리. ~, 렛스 리플레이싯 윗떠투
16. 1:24 in this case 1:30 but 1:40
~, y is 2 in this case, ~ but x is also now equal to 3.
17. 1:43 1:45 1:53
18. 1:59 2:00
.

분꽃나무
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the problem doesnt add up to 13 because 3 x 2 - 2 + 3 x 3 would change to 6 - 2 + 9. In pemdas it says addition goes before subtraction so it would be 9 + 2 = 11 which would be 6 - 11 = -5.

DuckLS
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This is in our science module im still thingking how science changed to math

joshuacarlcanlas
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Long story short: with addition and subtraction you can just go in order if that’s what’s left.

thejnus
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Is this channel sufficient for sat prep?

shivanshshekherojha
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The value of the letters?? Should we make it up by ourselves

sumaiyakhan
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What is confusing here is that the rules of multiplying was not explained very well! Because the order of operations has not been presented other than saying multiplication is the first order! Is multiplication is based on left to right?
Because why could it not be 3.3 = 9 then 2.3 =6
Then -2? = 14?

TheFalconJetDriver
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This answer is so wrong. The answer is 5. He did not follow the PEMDAS RULE I SEE THE COMMENTS SAYING SO TOO.

Solevi
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I still don’t get it this is, y second time watching this

nancycadreau