Answer Key — 1.NBT.C.5

For parents and tutors

Do not share with students before practice tests.

Practice Problems — Sets 1–10

| Set | Guidance | | --- | --- | | Set 1 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 2 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 3 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 4 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 5 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 6 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 7 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 8 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 9 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 10 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. |

Practice Problems — Sets 11–20

| Set | Guidance | | --- | --- | | Set 11 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 12 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 13 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 14 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 15 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 16 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 17 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 18 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 19 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. | | Set 20 | Given a two-digit number, mentally find 10 more or 10 less than the n… — verify written work and accept reasonable drawings. |

Review tiers 1–10

Checklists are parent-judged.
Written items: verify against practice set patterns.
Standard text: Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.

Practice test scoring

| Tier | Pass guidance | | --- | --- | | 1–3 | Most oral tasks smooth; majority of written correct | | 4–6 | 7/10+ total with clear understanding | | 7–8 | 9/12+ with explanations | | 9–10 | Near-perfect; ready to move on |

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