Math 7 · Unit 3, Lesson 4: Multiplying Signed Numbers · Tile 4 of 4
Real-World Products
Temperatures, dives, and money over time
The same change, again and again
Multiplying shows up whenever the same change happens again and again: the same drop every hour, the same cost every day. Give the change a sign, multiply by how many times it happens, and say what the answer means.
| Positive (+) | Negative (−) |
|---|---|
| earn | spend |
| deposit | withdraw |
| warmer | colder |
| rise | drop |
| up | down |
| above sea level | below sea level |
| time in the future | time in the past |
In a real-world product, the sign of the answer describes the direction of the total change.
If the answer is negative, things went down: colder, deeper, or less money. If it's positive, things went up.
Watch it work
A drilling rig digs down 2.5 meters every hour. Where is the drill after 15 hours?
The drill is at −37.5 meters, 37.5 meters below the ground.
A pond's water level drops 1.5 inches every day. How did the level 3 days ago compare to today? Three days ago is −3.
The water was 4.5 inches higher. Going back in time undoes the drops.
The drill problem is from the North Carolina unpacking document for this standard.
NC standard: NC.7.NS.2.