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    • ▾2nd grade
      • ▸Add and subtract within 20
        • •Add to count rectangular arrays
        • •Mentally add and subtract within 20
      • ▸Place value
        • •Place value with hundreds
        • •Convert between various representations, numbers within 1000
        • •Counting and skip-counting within 1000
        • •Intro to even and odd
        • •Compare three-digit numbers
      • ▾Add and subtract within 100
        • •Mentally add and subtract within 100
        • •Add and subtract within 100, abstract
        • •One-step word problems, add and subtract within 100
        • •Two-step word problems, add and subtract within 100
      • ▸Add and subtract within 1,000
        • •Add and subtract within 1,000
        • •Add multiple two-digit numbers
        • •Mentally add or subtract powers of ten
      • ▸Money and time
        • •Money word problems, including dollars
        • •Tell and write time, five minute increments
      • ▸Measurement
        • •Compare lengths by measuring
        • •Estimate lengths
        • •Add and subtract within 100 to solve word problems involving lengths
        • •Add and subtract within 100 on the number line
      • ▸Data
        • •Plot measurements on a line plot
        • •Draw picture and bar graphs
      • ▸Geometry
        • •Partition rectangles into rows and columns
        • •Area of a rectangle by counting unit squares
        • •Partition circles and rectangles into equal shares
        • •Draw shapes with certain attributes
        • •Intro to tessellations
     › 2nd grade › Add and subtract within 100

    Add and subtract within 100, abstract

    First, students will learn how to add two-digit numbers by adding the tens and ones separately. For example, \(52 + 43 = 50 + 40 + 2 + 3 = 90 + 5 = 95.\)

    Breaking apart 2-digit addition problems by Khan Academy

    Break apart 2-digit addition problems by Khan Academy

    Next, students will learn how to add two-digit numbers by making tens. For example, \(53 + 17 = 50 + 20 = 70.\)

    Watch these Khan Academy videos:

    • Adding 53+17 by making a group of 10
    • Adding by making a group of 10

    Add 2-digit numbers by making tens by Khan Academy

    After that, lead this investigation. Watch this to learn how. After students have found a couple blotches, get them to notice the numbers must add to the total number of squares in the grid. Conclude by leading this investigation. Watch this and this to learn how.

    Next, give your students this challenge:

    Make the equation below true by replacing each letter with a unique digit (0-9).

    $$BA = A \times A \times A$$

    Here's the solution:

    \(A \times A \times A = A^3.\) Thus, \(BA = A^3.\) Hence, \(BA\) is a two-digit cubed number, ending in \(A.\) By listing the first few cubes, we find \(3^3 = 27\) and \(4^3 = 64\) are the only two-digit cubed numbers, and only \(64 = 4^3\) fits \(BA = A^3.\) In conclusion, our equation is \(64 = 4 \times 4 \times 4.\)

    Conclude by leading this investigation:

    Puppet Puzzle (counting, logic, proof)
    by MathPickle

    2.NBT.B.5: Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.

    Additional lessons and practice problems