First Grade Mathematics
Unit 2
Numbers and Operations in Base Ten
Place Value

Printable Parent Letter

During Unit 2, your children will compare whole numbers (at least to 100) to develop understanding of and solve problems involving their relative sizes.  They will think of whole numbers between 10 and 100 in terms of tens and ones (especially recognizing the numbers 11 to 19 as composed of a ten and some ones).  Through activities that build number sense, they will understand the order of the counting numbers and their relative magnitudes.

Students need to:

  • 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.
  • Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases:
    • 10 can be thought of as a bundle of ten ones – called a "ten".
    • The numbers from 11 to 19 are composed of a ten and one, two, three, four, five six, seven, eight, or nine ones.
    • The numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two , three, four, five, six, seven, eight, and nine tens (and 0 ones)
  • Compare two two-digit numbers based on meanings of tens and ones digits, recording the results of comparisons with the symbols >, =, <.
  • Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
  • Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 – 4 = 13 – 3 – 1 = 10 – 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 – 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13). (continued from Unit 1)
  • Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem. (continued from Unit 1)
  • Solve word problems that call for addition of three whole numbers whose sum is less than or equal to 20, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem. (continued from Unit 1)
  • Organize, represent, and interpret data with up to three categories; ask and answer questions about the total number of data points, how many in each category, and how many more or less are in one category than in another. (continued from Unit 1)

Carroll County Public Schools Video Support

Comparing 2-Digit Numbers

Comparing Using Symbols

Using a Bar Graph

Ways Parents Can Help

  • Use blocks, pasta shapes or other fun objects to model numbers to 120. Have your child bundle groups of ten and identify how many tens and how many ones make up the number. Help your child to mentally find ten more and ten less than the number they built.
  • While riding in the car practice counting to 120, starting at any number less than 120.
  • Practice stating the number that is ten more or ten less than a given number. Have your child explain how they found the answer.
  • When seeing numbers in your surroundings, help your child to say them and tell how many tens and ones are in the number.
  • Use objects and/or drawings to represent and solve addition and subtraction word problems.
  • Encourage your child to use strategies to solve addition and subtraction facts within 20. Help your child to become fluent (answer orally within 3 seconds or less) with addition and subtraction facts within 10.
Some Support Sites


Key Vocabulary to Know















place value





two digit number