Answer Key — Lesson 4: Subtraction Strategies

Teacher answer key for all three versions of the Lesson 4 worksheet (subtraction strategies to four digits). ULO2.

Main — "Subtraction strategies to four digits"

1. a) 440   b) 750
2. 4 000 − 1 640 = 2 360 (count on: +60 to 1 700, +300 to 2 000, +2 000 to 4 000).
3. 3 250 − 1 480 = 1 770. Check: 1 770 + 1 480 = 3 250. ✓
4. 2 100 − 1 350 = 750 gumnuts given away.
5. 600 − 199 = 401. Take 200 (→400), then add 1 back (→401), because 199 is one less than 200, so we subtracted one too many and return it. Look for: the compensation explanation, not just the answer.

Support — "Subtraction by counting on"

1. a) 20   b) 30
2. a) 65   b) 60
3. 80 − 30 = 50
4. 50 + 20 = 70 (confirms 70 − 20 = 50).

Extension — "Harder subtraction and strategies"

1. a) 5 003 − 1 678 = 3 325   b) 8 200 − 3 645 = 4 555. Look for: (a) needs regrouping across zeros.
2. ☐ − 1 250 = 2 750, so ☐ = 4 000.
3. 4 200 − 1 850 = 2 350; 2 350 − 980 = 1 370 left. (Two steps shown.)
4. 700 − 397 = 303. Take 400 (→300), add 3 back (→303), since 397 is three less than 400.
5. Largest difference with 8,5,2,1 in ☐☐ − ☐☐: 85 − 12 = 73. Look for: biggest number minus smallest.