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2-Digit Mental Mathematics

Strand: Number
Outcomes: 6 and 7

Step 1: Identify Outcomes to Address

Guiding Questions

  • What do I want my students to learn?
  • What can my students currently understand and do?
  • What do I want my students to understand and be able to do, based on the Big Ideas and specific outcomes in the program of studies?

See Sequence of Outcomes from the Program of Studies

Strand: Number

Grade 2

Grade 3

Grade 4

Specific Outcomes
10.

Apply mental mathematics strategies, such as:

  • using doubles
  • making 10
  • one more, one less
  • two more, two less
  • building on a known double
  • thinking addition for subtraction

for basic addition facts and related subtraction facts to 18.

 

Specific Outcomes

6.

Describe and apply mental mathematics strategies for adding two 2-digit numerals, such as:

  • adding from left to right
  • taking one addend to the nearest multiple of ten and then compensating
  • using doubles.
7.

Describe and apply mental mathematics strategies for subtracting two 2-digit numerals, such as:

  • taking the subtrahend to the nearest multiple of ten and then compensating
  • thinking of addition
  • using doubles.
 

Specific Outcomes

5.

Describe and apply mental mathematics strategies, such as:

  • skip counting from a known fact
  • using doubling or halving
  • using doubling or halving and adding or subtracting one more group
  • using patterns in the 9s facts
  • using repeated doubling

to determine basic multiplication facts to 9 × 9 and related division facts.

Big Ideas

  • Computation is most efficient when supported by understanding.
  • There are strategies that make mental computation easier to perform.
  • Partitioning numbers in different ways can make mental computations easier to perform.
  • Two-digit numbers can be split into tens and ones and mental computations can be done on these parts before they are recombined to arrive at a solution.
  • Known facts, for example doubles, can be used in a variety of ways to help perform mental computations.
  • An understanding of the combinations that make 10 supports effective mental computations.
  • The ability to count by combinations of tens and ones supports effective mental computations.
  • Knowing doubles facts as they apply to 1-digit numbers supports an understanding of doubles of multiples of 10.
  • Understanding, memory and estimation sense are all supported when component parts with greater magnitude (the left-most columns in place value splitting) are operated on before those with lesser magnitude.
  • Thinking of the operations of addition and subtraction in terms of parts and wholes helps support mental computation and understanding.

Last Updated: May 30, 2012
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