Sal evaluates 2-step whole number expressions with different operations.
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- there are questions that i get wrong because i choose to do multiplication before division why is that?
shouldn't i be following PEMDAS?(18 votes)
- PEMDAS does not mean multiplication before division, even though it might appear that way. These two operations have equal priority and so should be done left to right. PEMDAS should really be presented as P E MD AS.(37 votes)
- One of the questions was 9-1+9+3 to the 4th power.
According to PEMDAS, I did:
9-1+9+81 (exponents first)
1+9=10 and 10+81=91 (addition next since no mult. or div.)
9-91=-82 (subtraction after addition)
but it was supposed to be 98.
How do we decide when we're supposed to do A & D from left to right and when we're supposed to follow PEMDAS?!(9 votes)
- You made a mistake in the third step. You have to go from right to left if the operation is the same. 9-1 is 8, 8+9 is 17, 17+81 is 98. You answer is 98. I don’t understand why you put an equal sign in the third step.(6 votes)
- How about someone says, "What is 2 divided 6 times 7". What do you do first?(9 votes)
- Multiplication and Division are equal operators and should be performed left to right.
So, you would perform 2/6 first, then multiply that result by 7.(7 votes)
- I was wondering, if you have 28/16-2 what would that be? The / is the same thing as a division. I'm just wondering if you understand the concepts.(6 votes)
- which one is first division or multiplacation?(3 votes)
- It depends on which comes first. For example 4/2*6 is 12 since 4/2 is 2 and 2*6 is 12. Another example is 6*3/9. You do 6*3 first since it comes first which is 18 and 18/9 is 2.(6 votes)
- [Instructor] If I were to ask you, what is five minus three plus two? What would you say that is? Pause this video and try to figure that out. All right, well if you wanted to tackle this, you would really just read it from left to right, or you would compute it from left to right. You'd first figure out what five minus three is, and five minus three is equal to two. And so you'd say, okay, that's going to be two plus two, which of course we know is equal to four. Now, what if I were to involve a little bit of multiplication or division? If I were to go up to you and I were to say, what is five plus three times two? Pause this video and try to figure that out. Well, you might be tempted to do it in a similar way. You might be tempted to say, okay, I'll just go from left to right. I'll first compute what five plus three is and that of course, would be equal to eight, and then I would multiply eight times two to get 16. But it turns out that this would not be the right way to approach this, because for very good reasons that we'll study in perhaps future videos, we don't always go left to right, especially when we're dealing with different types of operations. And the standard way that this is approached is that multiplication and division will be done before addition and subtraction. So the way that you would actually compute this is that you would compute the three times two first. So you would say that this is the same thing as five plus six, five plus six, which is going to be equal to 11, not 16. So this is going to be equal to 11. So with that out of the way, let's do a few more examples. Let's say someone were to approach you and say, what is nine minus six divided by three? Pause this video and see if you can figure that out. Well, as I just said, we would do multiplication or division before we do subtraction. So we'll actually do the six divided by three first, and six divided by three is two. So this simplifies to nine minus two, which is equal to seven, and I really wanna emphasize, it's important that you get this idea that multiplication and division should be done before the addition or subtraction, unless you're given some other types of directions. Because if you just went left to right here, you would have said nine minus six is three, and then you would've divided that by three, which would have given you one, which is clearly a different number than seven. Let's do one more example, just for kicks. Let's say that someone were to ask you, what is two times three minus one? Pause the video and try to figure that one out. Well, in this one, doing our multiplication first is also the same as going left to right first. So if we do two times three first, two times three is six, so that's six, and then we would wanna calculate six minus one, which is of course equal to five. So big picture, if you just have a bunch of things that are being added, subtracted, multiply, and divided, and there is no parenthesis in it, you would always prioritize the multiplication or the division over the addition or the subtraction.