Answer Key — Lesson 3: Adding Up to Four Digits

Teacher answer key for all three versions of the Lesson 3 worksheet (adding whole numbers to four digits). ULO2.

Main — "Combining the Gumnut Piles: Addition"

1. a) 590   b) 1 850
2. 2 350 + 1 425 = 3 775
3. a) 2 923   b) 6 030. Look for: both need carrying.
4. 1 850 + 2 340 = 4 190
5. Any valid pair summing to 5 000, e.g. 2 500 + 2 500, 3 200 + 1 800, 4 050 + 950. Look for: students show the two numbers add to exactly 5 000.

Support — "Adding, step by step"

1. a) tens 70, ones 8, total 78   b) tens 70, ones 7, total 77
2. a) 700   b) 550
3. 120 + 60 = 180
4. 1 200 + 300 = 1 500

Extension — "Bigger sums and addition puzzles"

1. a) 6 543   b) 10 217
2. 2 480 + 1 975 + 3 060 = 7 515
3. 2 350 + ☐ = 6 000, so ☐ = 3 650
4. Largest total from 1–6 in two 3-digit numbers: put the biggest digits in the hundreds. 631 + 542 = 1 173 (any arrangement with {6,5} in hundreds, {4,3} in tens, {2,1} in ones gives 1 173). Look for: 1 173 is the maximum; accept any digit split that reaches it.
5. True — two odd numbers always sum to an even number. Three correct examples (e.g. 3+5=8, 7+9=16, 11+13=24) and agreement.