Cogito
Grade 7 Math · Chapter 4 · Lesson 4
Signed Fractions and Decimals
The same rules, with messier numbers.
10 problems · about 19 minutes · 7.NS.A.1
What this lesson teaches
The child adds and subtracts negative fractions and decimals using the rules for integers.
- Sign rules do not change when the numbers are fractions or decimals.
- The number further from zero decides the sign of the answer.
- Estimate with whole numbers first to catch a sign error.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — The Additive Inverse: −5 − (−8) = ?
Answer 3
Why 3.
Review — Subtraction as Distance: 3 − (−8) = ?
Answer 11
Why 11.
Review — Adding Signed Numbers: −9 + 4 = ?
Answer -5
Why −5.
Warm Up
Straightforward practice. Get the method working first.
3 problems−3.5 + 1.25 = ?
Answer -2.25
Why −2.25.
−1.5 + 4 = ?
Answer 2.5
Why 4 is further from zero.
2.3 − 5.8 = ?
Answer -3.5
Why The answer is negative.
Build It Up
The same ideas with more to keep track of.
2 problems−0.5 + −0.75 = ?
Answer -1.25
Why Two negatives move further left.
−2.5 − (−4) = ?
Answer 1.5
Why −2.5 + 4.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Temperature: From −2.5 °C the temperature rises 4 °C. What is it now?
Answer 1.5
Why 1.5 °C.
The Drop: From 1.2 the value falls 3.7. What is it now?
Answer -2.5
Why −2.5.