Primary Standards:

MAFS.1.NBT.1.1 Count to 120, starting at any number less than 120.  In this range, read and write numerals and represent a number of objects with a written numeral.

MAFS.1.NBT.3.4 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.

MAFS.1.NBT.3.5 Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.

MAFS.1.NBT.3.6 Subtract multiples of 10 in the range 10–90 from multiples of 10 in the range 10–90 (positive or zero differences), 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.

Content Knowledge:

In prior unit, students learned about the place value of digits corresponding with tens and ones.  In this Unit, students will apply that understanding to work with adding and subtracting tens.  This Unit will focus students on realizing that when adding and subtracting, one must add or subtract tens with tens.  This focus on tens happens before the next Unit combining work with tens and ones because often working with ones will affect what is done with tens (when grouping a new ten, or the need for regrouping a ten into 10 ones is necessary.)

Students in Unit 1 began noticing patterns of counting on 10 more, or 10 less than a number.  This work will continue in the first GCG.  The goal of the standard is that students can focus on the patterns in our number system to mentally find 10 more or 10 less than any 2-digit number.  Hundred charts, ten frames, and base-ten blocks can help to reinforce this understanding and should be used to justify and connect to discover important ideas about the link between place value and computations.

Students then build upon these ideas to add multiples of 10 to any 2-digit number and subtract multiples of 10 from multiples of 10.  Again, manipulatives, drawings, hundred charts, and ten frames are helpful tools for exploring these processes.  Building on prior understanding of place value, for example that 30 is 3 tens, helps students’ model when adding or subtracting multiples of ten.


GCG 1 – Learning Goal: As a Mathematician, I will be able to Add and Subtract a Ten

  • Step 1: Add and Subtract 10 a Ten on a Hundred Chart (within 100)
  • Step 2: Add and Subtract a Ten on a Number Line (within 100)
  • Step 3: Use Patterns to Explain Adding and Subtracting a Ten to any two-digit number (within 100)

GCG 2 – Learning Goal: As a Mathematician, I will be able to Add Multiples of Ten

  • Step 1: Use Base Ten Block Models to Add Multiples of Ten to any two-digit number (within 100)
  • Step 2: Use Number Lines to Add Multiples of Ten to any two-digit number (within 100)
  • Step 3: Use Number Charts and Patterns to Explain Adding Multiples of Ten to any two-digit number (within 100)

GCG 3 – Learning Goal: As a Mathematician, I will be able to Subtract Multiples of Ten

  • Step 1: Use Base Ten Block Models to Subtract Multiples of Ten to any two-digit number (within 100)
  • Step 2: Use Number Lines to Subtract Multiples of Ten to any two-digit number (within 100)
  • Step 3: Use Number Charts and Patterns to Explain Subtracting Multiples of Ten to any two-digit number (within 100)