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## 7th grade (Illustrative Mathematics)

### Course: 7th grade (Illustrative Mathematics) > Unit 5

Lesson 8: Lesson 7: Adding and subtracting to solve problems# Negative number word problem: Alaska

In this video, we figure out the temperature in Fairbanks, Alaska by adding and subtracting negative numbers.

## Want to join the conversation?

- Who else dislikes word problems?(23 votes)
- im confused with the -5 and +2 does the +2 mean it goes to -11 or -7 and does the five mean you add -5 to get to -14 or -4.(10 votes)
- The plus two does mean the temperature goes up by two. The only reason this problem is confusing is that it gives you the temperature at the end of the changes, so you have to go backwards. That is why the signs of the +2 and -5 are reversed.(4 votes)

- I recommend watching the video to theend lol =)(5 votes)
- i dont understand any of these videos(0 votes)
- Go back to the previous videos an review how to add and subtract with negative numbers. This will help you to understand the videos.(28 votes)

- what do you do if you had to positive numbers what do you do(2 votes)
- what do you mean, can u plz give me more specificness in wat your trying to ask(3 votes)

- Which situation can be represented by the expression -2-5−2−5minus, 2, minus, 5?(3 votes)
- the temperature changed from 5 degrees celceis to 9 debrees celceis. what was the difference of the two?(0 votes)
- Please give more questions like these as such questions keep on appearing in SATs all over the globe.(2 votes)
- Why all i get is quiz 1 or quiz 2(2 votes)
- When we are asked a question, in which we are given a scenarios, and we are asked to answer relative to the surface of the water? What does this mean?(2 votes)

## Video transcript

- Amanda lives in Fairbanks, Alaska. The table below shows
the temperature changes in Fairbanks over a two-hour period. So when we went from 3pm to 4pm the temperature increased
by two degrees Celsius, and then from four to five the temperature decreased by five degrees Celsius. Amanda notices the temperature at 5pm is negative nine degrees Celsius. What was the temperature
in Fairbanks at 3pm? So they're essentially
telling us the temperature at the end of these changes, and they want us to
figure out the temperature at the beginning of these changes. So let's see if we can do that. Let me draw. Since, in thermometers we're
used to thinking vertically. So I'll draw a vertical number line here to think about this a little bit. So here we go. Alright, so at 5pm we end up at negative nine degrees Celsius, so let's just say this
is zero, negative one, two, three, four, five, six, seven, eight, nine. So we end up at negative
nine degrees Celsius. This is zero degrees
Celsius right over here. So from zero... Sorry, from 4pm to 5pm
the temperature dropped by five degrees Celsius and that got us to negative nine. So we drop by five to
get to negative nine, so we must've started
five above negative nine. So one, two, three, four, five... Right over here. So this is that drop. This is that five degree drop. Like we said, one, two, three, four, five. So that's that five degree
drop right over here. This is a negative five degrees Celsius. So at 4pm, right at 4pm, we
must've had a temperature of... Well, five above negative nine
is going to be negative four. Negative four degrees Celsius. This is what the temperature was at 4pm. So this is at 4pm. And then, to figure out 3pm, remember when we go from 3pm to 4pm our temperature increased
two degrees Celsius. So we increased by two
degrees Celsius from that hour to get to negative four degrees Celsius. So we increased by two degrees Celsius. So if we increase by two degrees Celsius to get to negative four, that means at 3pm we must've been two below that. So this is what we did from three to four. >From three to four we increased by two to get to negative four. So this right over here is
the plus two degrees Celsius right over there. So we must've started right here at 3pm. We must've started right there at 3pm. All I did is underline this. If you know we're at
negative nine to end with, and from four to five
we dropped negative five to get there, that means
at four we must've been five above negative nine. So we're at negative four, and then from three to four, if we increased two degrees to get there, that means at three we must've been two degrees below negative four. So this right over here is
negative six degrees Celsius. So what was the temperature
in Fairbanks at 3pm? It was negative six degrees Celsius. And you can verify that. If you start at negative six, you add two, you get to negative four, and then you subtract five,
you get to negative nine, which is exactly what we had here.