Add and Subtract Within 1000 - 3rd Grade Math

1. Emma needs to find $743 - 298$. What is the difference?
   Answer: 445 The difference is 445, since 743-298=445. Choice A (441) is 4 less than the correct answer, a likely subtraction slip. Choice B (443) is 2 less than the correct answer. Choice C (447) is 2 more than the correct answer.
2. Sofia is solving $526 + 387$. She breaks it down as $(500 + 300) + (20 + 80) + (6 + 7)$. What should she get for the final sum?
   Answer: 913 When you see a problem like this, you're working with place value and the strategy of breaking numbers apart to make addition easier. Sofia is using a smart approach by separating the hundreds, tens, and ones places. Let's follow Sofia's method step by step. She breaks $526 + 387$ into three separate additions: $(500 + 300) + (20 + 80) + (6 + 7)$. First, add the hundreds: $500 + 300 = 800$ Next, add the tens: $20 + 80 = 100$ Finally, add the ones: $6 + 7 = 13$ Now combine all these parts: $800 + 100 + 13 = 913$ So the correct answer is C) 913. Let's see where the other answers might come from. Answer A) 813 happens if you forget to add the tens properly—maybe calculating $20 + 80 = 0$ instead of $100$. Answer B) 903 occurs if you make an error with the ones place, perhaps thinking $6 + 7 = 3$ instead of $13$. Answer D) 923 results from an error in the tens place, possibly calculating $20 + 80 = 110$ instead of $100$. Remember this strategy: when breaking apart numbers by place value, always double-check each step before combining your partial sums. It's also helpful to estimate first—both numbers are in the hundreds, so your answer should be in the 900s, which immediately rules out answer A.
3. The library had 500 books. 237 books were checked out. How many books are left?
   Answer: 263 books Subtracting 237 from 500 gives 263 books remaining. Choice B and Choice C both come from subtraction errors involving the hundreds and tens digits. Choice D comes from a similar subtraction slip in the ones place.
4. A community center packed 642 meals. They gave 387 meals to families. How many meals remain?
   Answer: 255 meals 255 meals is correct because 642 minus 387 equals 255. 265 meals is incorrect because it does not match subtracting 387 from 642. 355 meals is incorrect because it does not match the correct difference. 1,029 meals is incorrect because it adds the two numbers instead of subtracting them.
5. Amir needs 650 tickets for a prize. He already has 385 tickets. How many more tickets are needed?
   Answer: 265 tickets Subtracting 385 from 650 gives 650 minus 385, which is 265 tickets. Choice A, 1,035 tickets, comes from adding the two ticket counts instead of subtracting. Choice C, 365 tickets, comes from an error in regrouping during subtraction. Choice D, 275 tickets, comes from a small subtraction error.
6. Maya collected 429 shells on Saturday and some shells on Sunday. After giving 158 shells to her sister, she had 394 shells left. How many shells did Maya collect on Sunday?
   Answer: 123 Maya had 394 shells left plus the 158 she gave away, which is 552 total shells, and subtracting the 429 she collected Saturday leaves 123 shells collected Sunday. Choice B (265) comes from subtracting 158 from 429 instead of solving for Sunday's shells. Choice C (271) comes from subtracting 429 from 394 without accounting for the shells given away, then adjusting incorrectly. Choice D (552) is the total shells before giving any away, not the amount collected on Sunday.
7. Maya had 458 stickers. She got 276 more stickers and gave away 139 stickers. How many stickers does she have now?
   Answer: 595 stickers Maya's total after receiving more stickers is 458 plus 276, which is 734, and after giving away 139, she has 734 minus 139, which is 595 stickers, matching choice B. Choices A and C reflect small errors in the subtraction step. Choice D stops after the addition and never subtracts the stickers she gave away.
8. Maya had 458 stickers. She got 276 more stickers and gave away 139 stickers. How many stickers does she have now?
   Answer: 595 stickers Adding 458 and 276 gives 734 stickers, and subtracting the 139 given away leaves 595 stickers. Choice A (585 stickers) comes from a subtraction error after finding the correct sum. Choice B (605 stickers) is off by ten from the correct total. Choice D (734 stickers) is the sticker count before any were given away, not the final amount.
9. Read the problem. Sofia read 185 pages Monday, 236 pages Tuesday, and 147 pages Wednesday. What is the total number of pages?
   Answer: 568 pages This question tests fluent addition and subtraction within 1000 (CCSS.3.NBT.2), specifically using strategies and algorithms based on place value and regrouping. To add 3-digit numbers, line up place values (ones, tens, hundreds). For addition: Add ones (if sum ≥10, regroup to tens), add tens (if sum ≥10, regroup to hundreds), add hundreds. For subtraction: Subtract ones (if can't, borrow from tens), subtract tens (if can't, borrow from hundreds), subtract hundreds. Example: 347+286: Start with ones (7+6=13, write 3 carry 1), then tens (4+8+1=13, write 3 carry 1), then hundreds (3+2+1=6), answer 633. For subtraction across zero like 500-237: Need to borrow: 500 becomes 4 hundreds, 10 tens, 0 ones. Then 10-7=3, 9-3=6 (after borrowing 1 from tens to make 10 ones), 4-2=2, answer 263. In this problem, Sofia read 185 pages Monday, 236 Tuesday, and 147 Wednesday, asking for the total pages. This requires addition of three numbers with regrouping in multiple places. Choice A is correct because 185 + 236 + 147 = 568. This demonstrates proper place value alignment, regrouping when needed, multi-step execution. Choice B represents the error of adding only two numbers (185 + 236 = 421) and forgetting the third. This happens when students overlook multi-step additions. To help students with addition/subtraction within 1000: Use place value charts or base-10 blocks to visualize regrouping. Practice expanded form (347 = 300+40+7). Teach borrowing across zero explicitly (500 = 4 hundreds, 10 tens, 0 ones). Emphasize lining up place values vertically. Check answers with estimation (347+286 is about 350+300=650, so 633 reasonable). Practice both with and without regrouping. Watch for students who don't carry/borrow correctly or who apply operations inconsistently across place values.
10. A parking garage has 3 levels. Level 1 has 178 cars, Level 2 has 94 fewer cars than Level 1, and Level 3 has 126 cars. How many cars are in the garage total?
    Answer: 388 Level 2 has 178 minus 94, which is 84 cars, so the total is 178 plus 84 plus 126, which is 388 cars. Choice A (398) comes from adding 178, 94, and 126 directly, treating 94 as Level 2's actual car count instead of subtracting it from Level 1. Choice C (304) comes from adding only Level 1 and Level 3, leaving Level 2 out entirely. Choice D (272) comes from adding Level 1's cars and the 94-car difference while leaving out Level 3 entirely.
11. A community center packed 642 meals. Then 387 meals were delivered. How many meals remain?
    Answer: 255 meals Subtracting 387 delivered meals from 642 packed meals gives 642 minus 387, which is 255 meals, matching choice A. Choices B and C reflect small errors in the subtraction. Choice D adds the two numbers instead of subtracting them.
12. Read the problem. The school library had 500 books. 237 books were checked out. How many books are left?
    Answer: 263 books This question tests fluent addition and subtraction within 1000 (CCSS.3.NBT.2), specifically using strategies and algorithms based on place value and regrouping. To add 3-digit numbers, line up place values (ones, tens, hundreds). For addition: Add ones (if sum ≥10, regroup to tens), add tens (if sum ≥10, regroup to hundreds), add hundreds. For subtraction: Subtract ones (if can't, borrow from tens), subtract tens (if can't, borrow from hundreds), subtract hundreds. Example: 347+286: Start with ones (7+6=13, write 3 carry 1), then tens (4+8+1=13, write 3 carry 1), then hundreds (3+2+1=6), answer 633. For subtraction across zero like 500-237: Need to borrow: 500 becomes 4 hundreds, 10 tens, 0 ones. Then 10-7=3, 9-3=6 (after borrowing 1 from tens to make 10 ones), 4-2=2, answer 263. In this problem, the school library had 500 books and 237 were checked out, asking how many are left. This requires subtraction with borrowing across zero in the tens and ones places. Choice A is correct because 500 - 237 = 263. This demonstrates proper borrowing correctly across zero. Choice B represents the error of subtracting smaller from larger in each place without borrowing, resulting in 337. This happens when students don't borrow properly. To help students with addition/subtraction within 1000: Use place value charts or base-10 blocks to visualize regrouping. Practice expanded form (347 = 300+40+7). Teach borrowing across zero explicitly (500 = 4 hundreds, 10 tens, 0 ones). Emphasize lining up place values vertically. Check answers with estimation (347+286 is about 350+300=650, so 633 reasonable). Practice both with and without regrouping. Watch for students who don't carry/borrow correctly or who apply operations inconsistently across place values.
13. Marcus scored 425 points in the first game and 386 points in the second game. How many points did he score altogether?
    Answer: 811 points Marcus scored 425 + 386 = 811 points altogether, so Choice B is correct. Choice A (39 points) comes from subtracting instead of adding, 425 - 386 = 39. Choice C (711 points) and Choice D (801 points) come from addition errors, such as misaligning place values when adding the hundreds, tens, and ones.
14. Emma collected 347 cans in October and 286 cans in November. How many cans did she collect in all?
    Answer: 633 cans Emma collected 347 + 286 = 633 cans in all, so Choice A is correct. Choice B (61 cans) comes from subtracting instead of adding, 347 - 286 = 61. Choice C (523 cans) and Choice D (632 cans) come from addition errors, such as misaligning place values when adding the hundreds, tens, and ones.
15. Read the problem. Maya walked 784 steps in PE. Marcus walked 659 steps. How many more steps does Maya have than Marcus?
    Answer: 125 steps This question tests fluent addition and subtraction within 1000 (CCSS.3.NBT.2), specifically using strategies and algorithms based on place value and regrouping. To add 3-digit numbers, line up place values (ones, tens, hundreds). For addition: Add ones (if sum ≥10, regroup to tens), add tens (if sum ≥10, regroup to hundreds), add hundreds. For subtraction: Subtract ones (if can't, borrow from tens), subtract tens (if can't, borrow from hundreds), subtract hundreds. Example: $347 + 286$: Start with ones ($7 + 6 = 13$, write 3 carry 1), then tens ($4 + 8 + 1 = 13$, write 3 carry 1), then hundreds ($3 + 2 + 1 = 6$), answer 633. For subtraction across zero like $500 - 237$: Need to borrow: 500 becomes 4 hundreds, 10 tens, 0 ones. Then $10 - 7 = 3$, $9 - 3 = 6$ (after borrowing 1 from tens to make 10 ones), $4 - 2 = 2$, answer 263. In this problem, Maya walked 784 steps and Marcus 659, asking how many more Maya has. This requires subtraction with borrowing in the ones place. Choice A is correct because $784 - 659 = 125$. This demonstrates proper borrowing correctly. Choice B represents the error of not borrowing in the ones place, resulting in 135. This happens when students subtract without adjusting for borrowing. To help students with addition/subtraction within 1000: Use place value charts or base-10 blocks to visualize regrouping. Practice expanded form ($347 = 300 + 40 + 7$). Teach borrowing across zero explicitly (500 = 4 hundreds, 10 tens, 0 ones). Emphasize lining up place values vertically. Check answers with estimation ($347 + 286$ is about $350 + 300 = 650$, so 633 reasonable). Practice both with and without regrouping. Watch for students who don't carry/borrow correctly or who apply operations inconsistently across place values.
16. A community center packed 642 meals. Then 387 meals were delivered. How many meals remain?
    Answer: 255 meals 255 meals is correct because $642 - 387 = 255$. 355 meals is incorrect; it doesn't match the correct subtraction. 1,029 meals is incorrect because it comes from adding 642 and 387 instead of subtracting. 265 meals is incorrect; it doesn't correspond to $642 - 387$.
17. Marcus collected 247 stickers in January and 389 stickers in February. He gave away 156 stickers to his friends. How many stickers does Marcus have left?
    Answer: 480 stickers First, add the stickers collected: 247 + 389 = 636. Then subtract the stickers given away: 636 - 156 = 480. Choice B shows only the addition step. Choice C shows adding all three numbers instead of subtracting. Choice D shows subtracting 156 from 247 and adding 389.
18. Marcus scored 458 points in the first game and 367 points in the second game. How many points did he score altogether?
    Answer: 825 points Adding 458 and 367 gives a total of 825 points. Choice A (725 points) comes from an addition error in the hundreds place. Choice C (815 points) is off by ten from the correct total. Choice D (91 points) comes from subtracting instead of adding the two scores.
19. A school library had 584 books. They bought 127 new books and donated 95 old books to charity. Which expression shows how to find the total number of books the library has now?
    Answer: $584 + 127 - 95$ Start with 584 books, add 127 new books, then subtract 95 donated books: 584 + 127 - 95. Choice B incorrectly subtracts the new books and adds the donated books. Choice C adds all numbers without considering donation. Choice D subtracts both the new books and donated books.
20. Sofia needs 650 points to earn a prize. She already has 285 points. How many more points does she need?
    Answer: 365 points 365 points is correct because $650 - 285 = 365$. 335 points is incorrect; it doesn't match the correct subtraction. 275 points is incorrect because it doesn't correspond to $650 - 285$. 935 points is incorrect; it comes from adding 650 and 285 instead of subtracting.

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