7th grade (Illustrative Mathematics)
The examples in this video use negative numbers to represent real world situations. What are these negative numbers really telling us?
Want to join the conversation?
- so below=subtraction/negative
and above=addition/positive?(10 votes)
- Yes. The numbers below zero are negative/subtraction, and the numbers above are addition/positive.(3 votes)
- why was the first question the letter (B)?(4 votes)
- the first question was (B) because the first one had an addition in it and the second was adding negatives which is the same as subtracting. So we won't choose (C) because we found a answer.(0 votes)
- I just started this math and I thought it would be great. It was fine untill last lesson. The reason I changed to a different math was because it didn't explain reducing and simplifying. This as far as I can tell doesn't ether. Am I missing a lesson?(1 vote)
- You can search for something here on simplifying and reducing. I think there are some vids on that but I'm not sure.(1 vote)
- [Voiceover] Lina was watching a football game. The team she was cheering for gained six yards on one play. It lost eight yards on the next play. It lost another two yards on the following play. Lina wants to know what her team's net change in field position was after these three plays. Which of the following equations matches the situation above? So, let's think about it. The team she was cheering for, first they gained six yards. So that's positive six yards. Then they lost eight. So it'd be six minus eight. And then it lost another two. So, six minus eight minus two. This is six minus eight but then plus two. So, this isn't right. This is six plus negative eight which is equivalent to six minus eight, plus negative two. So, this would be equivalent to six minus eight minus two. Or another way to think about it, they gained six yards. Then they lost eight yards. And then they lost another two yards. So, definitely go with that one. Let's keep going. Eddie and Fran are scuba diving. Eddie is 35 meters below the surface of the water, and Fran is eight meters directly above him. The following situation describes this, or the following equation describes this situation. So let's see, Eddie is 35 meters below the surface of the water. So, when we're below the surface, or the more below the surface we are, the more negative, I guess is what we're doing here. So, if we're at the surface of the water, you would be at zero meters. And they tell us Fran is eight meters above him. So we're taking Eddie's depth at 35 meters and then Fran is eight meters above. So, we're adding eight, to figure out Fran's depth of negative 27 meters. Notice, this is eight meters above Eddie's depth. So, negative 27 is Fran's depth. She is 27 meters below the surface of the water. So, select all that apply. Fran is 27 meters below the surface of the water. Yeah, that's what we just talked about. If your depth is, or I guess you could say, if you're at negative 27 that means 27 meters below the water. If you were at positive 27, that means you're at 27 meters above the water. So that's what they're telling us. Fran's position relative to the surface of the water is negative 27 meters. Yeah, I think that's a reasonable way to say it. It's a little bit more confusing. But, yeah, she is negative 27 meters below the surface of the water which we just said up here. So I think that's fair enough to say that as well. Let's do one more. Fred's basement is flooded. The basement floor is 3.4 meters below the ground floor. Alright, that makes sense that the basement is below the ground, 3.4 meters. The water is 1.2 meters high. The following equation describes this situation. So negative 3.4, that's where the floor of the basement is. It is 3.4 meters below the ground floor. So the ground floor would be zero. So, it's 3.4 meters below the ground floor. So, that's the negative 3.4. But then the water is 1.2 meters. The top of, the surface of the water, is 1.2 meters above the floor of the basement. So this negative 2.2 is how high the top of the water is. So, what does negative 2.2 tell us? Well, the top of the water is 2.2 meters below the ground floor. Yep, that's right. The water's 1.2 meters above the floor of the basement which is negative 2.2 meters. And this is all relative to the ground floor. So if the ground floor was zero, the top of the water is negative 2.2, which means the top of the water is 2.2 meters below, that's what the negative tells us, below the ground floor. The water is 2.2 meters deep. No, that's not right. They tell us that the water is 1.2 meters high or 1.2 meters deep. So, that's not right. And we're not going to click None of the above because we definitely found, we found an answer.