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    • ▾1st grade
      • ▸Place value
        • •Count and write numbers within 120
        • •Skip count by 3s and 4s
        • •Place value with tens
        • •Compare two-digit numbers
      • ▾Addition and subtraction
        • •River crossing puzzles
        • •Add and subtract within 20
        • •Add within 20, word problems involving three addends
        • •Use one addition problem to solve another
        • •Add by making tens
        • •Subtract by adding
        • •Understand the equals sign
        • •Add and subtract within 20, missing number problems
        • •Add and subtract within 20, word problems
        • •Add within 100, concrete and pictorial
        • •10 more or 10 less
        • •Subtract multiples of ten from multiples of ten
      • ▸Measurement, data, and geometry
        • •Order without tools
        • •Measure given a unit
        • •Bar and picture graphs having three categories of data
        • •Tell and write time, hour and half-hours
        • •Definitions of shapes
        • •Compose 2D and 3D shapes
        • •Halves and quarters
     › 1st grade › Addition and subtraction

    10 more or 10 less

    Students will learn how to find 1 more, 1 less, 10 more, or 10 less. To find 10 more or 10 less, the units stay the same, only the tens place changes. Students should not count to find 10 more, or 10 less. For example, to find 10 less than 46, students should not count 46, 45, ..., 36.

    Adding 1 vs. adding 10 by Khan Academy

    Add 1s or 10s (no regrouping) by Khan Academy

    Next, give your students this challenge:

    2018 Math Kangaroo Levels 1-2 Problem #18 by STEM4all

    Conclude by leading this investigation:

    Cannibal Fish
    by MathPickle

    1.NBT.C.5: Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.

    Additional lessons and practice problems