1.NBT.C.4 — Adding Within 100 Using Place Value

1.NBT.C.4 is a first grader's introduction to the idea that tens and ones behave differently. Adding thirty to a number changes one digit and leaves the other alone, and noticing that is worth more here than getting the answer. The standard's closing line — that sometimes it is necessary to compose a ten — is the seed of every regrouping problem in the years that follow.

The standard, word for word

Quoted verbatim from the Common Core State Standards for Mathematics. Nothing here is paraphrased.

1.NBT.C.4	Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones; and sometimes it is necessary to compose a ten.

1.NBT.C.4

Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones; and sometimes it is necessary to compose a ten.

In plain English: Add within 100 — a two-digit number plus a one-digit number, or plus a multiple of ten — using place value, and explain the reasoning.

Free Grade 1 activities that practice 1.NBT.C.4

Each one runs in the browser with no account and nothing stored. Five questions apiece.

Adding tens within 100Grade 1 · 1.NBT.C.4

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What 1.NBT.C.4 looks like as a question

Real output from the activities above — not written for this page, drawn from the same pools a student gets. The numbers are rebuilt on every attempt.

🔐 Adding tens within 100 — Crack the Airlock

60 + 16 = ?	76
30 + 27 = ?	57
50 + 16 = ?	66

🎉

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