Wyoming Math 2.OA.2
The Standard
Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know automatically all sums of two one-digit numbers based on strategies.
2023 Wyoming Mathematics Content and Performance Standards · Add and subtract within 20.
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students add and subtract within 20 in their heads. They use moves like making ten, doubles, and related facts, and learn to recall sums of two one-digit numbers.
What Mastery Looks Like
- A student answers 6 + 7 quickly without counting one by one. They use 8 + 7 = 15 to work out 15 − 8 = 7.
Common Misconceptions
- Some students count from one for every problem, even when they know a helpful fact. Others think 8 + 7 and 15 − 8 are unrelated, or switch the numbers in a subtraction problem.
How to Assess It
- On an exit ticket, ask students to solve 8 + 7, 15 − 8, and 6 + 7 without counting marks. Have them write one mental step they used.
Lesson moves
Ways to Teach It
Give pairs ten-frames and counters to build 8 + 7, then move two counters from the seven to make ten.
Ask, 'How can 8 + 7 help you solve 15 − 8?' Have students write one sentence and compare with a partner.
Show 6 + 7 on a flash card for three seconds, then ask students to say the sum and name a mental shortcut.
Give students pretend $20 bills and snack prices of $8 and $7; ask them to find the total and change mentally.
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Printable 2.OA.2 Worksheet
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Related Standards
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- 3.OA.7
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