Add & Subtract Within 1000 — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. If 345 + ___ = 520, which subtraction checks the missing number?
A) 520 - 345
B) 345 - 520
C) 520 + 345
D) 345 + 520
520 - 345 = 175, so 520 - 345 is the inverse check for the missing addend.
2. Mia says 648 - 273 = 375. Which addition checks her work?
A) 375 + 273
B) 648 + 375
C) 648 + 273
D) 375 - 273
If the answer is right, 375 + 273 should equal 648, confirming the subtraction.
3. If 186 + 429 = 615, which subtraction proves 615 is correct?
A) 615 - 429
B) 615 + 186
C) 186 - 429
D) 429 + 186
615 - 429 should give 186, which proves the original addition.
4. Leo solved 702 - 348 = 354. Which check confirms his answer is right?
A) 354 + 348 = 702
B) 702 + 348 = 354
C) 354 - 348 = 702
D) 348 - 354 = 702
354 + 348 = 702 matches the original total, confirming the difference.
Part B: Fill in the Blank
Write the correct answer on each line.
1. To check 267 + ? = 500, compute 500 - 267 = 233
500 - 267 = 233, which equals the missing addend.
2. Check 814 - 236 = 578 by computing 578 + 236 = 814
578 + 236 = 814 matches the starting number, so the subtraction is correct.
3. Check 145 + 329 = 474 by computing 474 - 145 = 329
474 - 145 = 329, matching the other addend and proving the sum.
4. Check 603 - 258 = 345 by computing 345 + 258 = 603
345 + 258 = 603, the original number, confirming the subtraction.
5. To check 392 + ? = 700, compute 700 - 392 = 308
700 - 392 = 308, which is the missing addend.