Math 7 · Unit 3, Lesson 3: Signed Fractions and Decimals · Tile 3 of 3
Real Money, Real Problems
Bank accounts, temperatures, and dives
Put the signs in
Real problems don't come with plus and minus signs. You have to put them in. Money in, warmer, and up are positive. Money out, colder, and down are negative. Write the problem as one long adding problem, then use everything you know.
Represent each quantity in the situation with a signed number, write a single expression, and evaluate it.
Give every number a sign that matches the story. Then it's just an adding problem.
Watch it work
Justin wants a video game that costs $54.79. He started the day with $210 in his bank account. He spent $87.35 at a clothing store, $42.79 at a party store, and $25.68 at a gas station. Does he have enough for the game?
Estimate to check. 210 minus about 155 is about 55, and the game is about 55. Too close to call by estimating, so the exact math matters here.
Give it a sign
| Positive (+) | Negative (−) |
|---|---|
| earn | spend |
| deposit | withdraw |
| warmer | colder |
| rise | drop |
| up | down |
| above sea level | below sea level |
NC standard: NC.7.NS.1.