Cogito
Grade 6 Math · Chapter 3 · Lesson 5
Adding and Subtracting Decimals
Line up the point, not the digits.
10 problems · about 17 minutes · 6.NS.B.3
What this lesson teaches
The child adds and subtracts multi-digit decimals fluently.
- Line up the decimal points, not the last digits.
- Fill short numbers with zeros so both have the same length.
- Estimate first, so a misplaced point is obvious.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Dividing Multi-Digit Numbers: 468 ÷ 18 = ?
Answer 26
Why 26.
Review — Common Factors and Common Multiples: Greatest common factor of 16 and 40?
Answer 8
Why 8.
Review — Multiplying and Dividing Decimals: 9 ÷ 0.3 = ?
Answer 30
Why 30.
Warm Up
Straightforward practice. Get the method working first.
3 problems6.4 + 2.75 = ?
Answer 9.15
Why 9.15.
2.4 + 1.35 = ?
Answer 3.75
Why 2.40 + 1.35.
5.6 − 2.45 = ?
Answer 3.15
Why 5.60 − 2.45.
Build It Up
The same ideas with more to keep track of.
2 problems0.3 + 0.05 = ?
Answer 0.35
Why Thirty hundredths and five hundredths.
7 − 3.25 = ?
Answer 3.75
Why Write 7 as 7.00.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Shopping: £3.45 and £2.30 together, in pounds?
Answer 5.75
Why £5.75.
The Change: £10 minus £6.40, in pounds?
Answer 3.6
Why £3.60.