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Mental Math Addition and Subtraction within 20 Number Puzzles

Tessa Maguire
Grade Levels
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20 pages
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Tessa Maguire


These Addition and Subtraction within 20 Number Puzzles present students with a number to make using addition and/or subtraction given another set of numbers. Each number has multiple possible combinations, building mathematical discourse in your classroom as students explain how they came to their solution and expand on their peer's understanding. This activity builds number sense and mental math skills through whole class or small group math discourse.

Number sense and mental math are such crucial skills to build in the early years. Working with and manipulating numbers without paper builds students' understanding of the numbers, and their ability to work through math problems quickly and successfully later.

A set of answers is included to help you see potential combinations and guide your students through new ways of using the numbers. Most solutions have combinations that include using addition and subtraction, helping strengthen students understanding of the operations.

Help build your students mental math skills and number sense in just a few minutes each day.

Total Pages
20 pages
Answer Key
Teaching Duration
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to see state-specific standards (only available in the US).
Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 - 4 = 13 - 3 - 1 = 10 - 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 - 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).
Apply properties of operations as strategies to add and subtract. If 8 + 3 = 11 is known, then 3 + 8 = 11 is also known. (Commutative property of addition.) To add 2 + 6 + 4, the second two numbers can be added to make a ten, so 2 + 6 + 4 = 2 + 10 = 12. (Associative property of addition.)
Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones; and sometimes it is necessary to compose a ten.


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