# 2.OA.B.2*

Add and subtract within 20.  Fluently add and subtract within 20 using mental strategies.1 By end of Grade 2, know from memory all sums of two one-digit numbers.

*TNCore Focus Standard

## Summary:

Students need a variety of strategies for solving addition and subtraction problems through 20. These strategies will provide students with a variety of choices when deciding the best way to solve problems mentally and give them practice in fluid (quick and accurate) problem solving. Students should know all the sums of two one-digit numbers from memory by the end of the school year.

## Understanding the Standard:

• Flash cards can be used for memorizing sums of two one-digit numbers. (0 + 0 through 9 + 9).
• Picture representations of numbers can be used to help visualize and memorize sums of two one-digit numbers. (Ten frames of the facts 0 + 0 through 10 + 10).
• Games that encourage speed and accuracy of sums of two one-digit numbers can make memorization fun.
• With fluency in one digit sums, students can then mentally add and subtract within 20. For example, 20 – 12 becomes “20 minus 10 is 10, and two less is 8.”

## Questions to Focus Instruction:

• Can students solve problems through 20 quickly in their heads, without pencil and paper?
• Do students know (i.e., have memorized) all their sums of two one-digit numbers?
• Can students mentally solve addition and subtraction problems within 20?

## Skills

Prior to: Students will demonstrate mastery in solving addition and subtraction problems through 20. They will use a variety of strategies and will explain their reasoning and process for doing so. Go to 1.OA.C.6 to see previous skills in this progression.

At Grade Level: Students can fluently add and subtract through 20 using mental strategies. Students have memorized all sums of two one-digit numbers by the end of the school year.

Moving Beyond: Students will move on to fluently add and subtract within 1000 using a variety of strategies, knowledge of place value and properties of operations. Go to 3.OA.C.7. to see the progression of related skills.

1See standard 1.OA.6 for a list of mental strategies.