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150 multiple-choice questions, 50 flashcards and 10 scenario simulations, written to the Common Core State Standards blueprint. Every question carries a full rationale.
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Common Core State Standards (CCSS) — Mathematics, Grade 3: Number & Operations in Base Ten (3.NBT.A.1-3). Public standards from corestandards.org.
CoStudy's 3rd Math: Number & Operations Base Ten bank holds 210 items. Every multiple-choice question carries a written rationale explaining why the correct answer is correct and why each distractor is tempting but wrong, and the bank includes 10 scenario-based simulations.
A sample of 12 multiple-choice questions from the bank, with the full rationale shown.
617 + 82 = ?
Answer: D — 699
D) Correct — 7+2=9, 1+8=9, 6+0=6 → 699. B) miscarry. C) miscarry. A) missed hundreds.
Round 613 to the nearest 10.
Answer: A — 610
A) Correct — 3 < 5, round down. B) wrong direction. C) that's nearest 100. D) not multiple.
What is 5 × 90?
Answer: A — 450
5 × 9 = 45 → × 10 = 450. (B),(C),(D) wrong.
1000 − 456 = ?
Answer: A — 544
A) Correct — 1000−456=544. B/C) miscount. D) miscount hundreds.
A box has 50 candies. 6 boxes contain how many?
Answer: B — 300
6 × 50 = 300. (A),(C),(D) wrong.
761 − 289 = ?
Answer: D — 472
D) Correct — 761−289=472. B/C) miscount. A) miscount hundreds.
800 − 375 = ?
Answer: A — 425
A) Correct — 800−375=425. B/C) miscount. D) miscount hundreds.
584 + 273 = ?
Answer: C — 857
C) Correct — 4+3=7, 8+7=15, 5+2+1=8 → 857. B/A) miscarry. D) subtracted top.
Round 305 to the nearest 100.
Answer: D — 300
D) Correct — tens 0 < 5, round down. B) wrong direction. C) that's nearest 10. A) not multiple.
742 − 356 = ?
Answer: A — 386
A) Correct — 742−356=386. B/C) miscount. D) miscount hundreds.
123 + 456 = ?
Answer: D — 579
D) Correct — 3+6=9, 2+5=7, 1+4=5 → 579. B/C) miscarry. A) miscarry hundreds.
178 + 823 = ?
Answer: D — 1001
D) Correct — 8+3=11, 7+2+1=10, 1+8+1=10 → 1001. B) miscarry. C) missed hundreds. A) miscarry.
6 sample cards from the 50 in the bank.
Round 145 to the nearest 10.
150.
What is 5 × 70?
350.
Round 47 to the nearest 10.
50. (Ones digit 7 ≥ 5, round up.)
What is 845 − 327?
518.
What is 500 − 367?
133.
What is 354 + 196?
550.
These samples are a small slice. The full bank runs flashcards, multiple choice and timed mock exams with per-chapter progress tracking, on the web and in the iOS app.
Open 3rd Math: Number & Operations Base Ten →
The 3rd Math: Number & Operations Base Ten bank holds 210 items: 150 multiple-choice questions, 50 flashcards and 10 scenario-based simulations. 18 of them are on this page to read free, with no signup.
Yes. Every multiple-choice item carries a written rationale that states the controlling principle behind the correct answer and then addresses each wrong option in turn — why it tempts and precisely where it fails. Knowing why the plausible answer was wrong is worth more than knowing which letter was right.
Common Core State Standards (CCSS) — Mathematics, Grade 3: Number & Operations in Base Ten (3.NBT.A.1-3). Public standards from corestandards.org.
The samples on this page are free to read in full, rationales included, with no account. The complete 210-item bank, the timed mock exams and per-chapter progress tracking are part of CoStudy on the web and in the iOS app.
Last reviewed 2026-08-22. Banks are written against the certifying body's published exam outline and re-checked when that outline changes — exams get renumbered, retired and reweighted, and a bank written to a superseded outline teaches the wrong proportions. Figures that are re-indexed annually are deliberately not asserted as rules; the questions test the governing principle instead.