In this activity, students will demonstrate their ability to use a variety of strategies to mentally solve subtraction problems. Understanding the way these strategies work helps build students’ number sense, flexibility with numbers, and confidence in manipulating numbers in a variety of ways. Students will learn, review, and practice using four subtraction strategies before showing their strategy skills on a mini quiz.
MP2 | Reason abstractly and quantitatively. |
MP3 | Construct viable arguments and critique the reasoning of others. |
MP7 | Look for and make use of structure. |
MP8 | Look for and express regularity in repeated reasoning. |
CCSS.Math.Content.1.OA.B.3 – Apply properties of operations as strategies to add and subtract. Examples: 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.) |
CCSS.Math.Content.1.OA.B.4 – Understand subtraction as an unknown-addend problem. For example, subtract 10 - 8 by finding the number that makes 10 when added to 8. |
CCSS.Math.Content.1.OA.C.5 – Relate counting to addition and subtraction (e.g., by counting on 2 to add 2). |
CCSS.Math.Content.1.OA.C.6 - 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). |
CCSS.Math.Content.1.NBT.B.2.A – Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases: 10 can be thought of as a bundle of ten ones — called a "ten." |
CCSS.Math.Content.1.NBT.B.2.B – Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases: The numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones. |
CCSS.Math.Content.1.NBT.B.2.C – Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases: The numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens (and 0 ones). |
CCSS.Math.Content.1.NBT.C.5 – Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used. |
CCSS.Math.Content.1 NBT.C.6 – Subtract multiples of 10 in the range 10-90 from multiples of 10 in the range 10-90 (positive or zero differences), 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. |
CCSS.Math.Content.2.OA.B.2 - Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know from memory all sums of two one-digit numbers. |
CCSS.Math.Content.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. |
CCSS.Math.Content.2.NBT.B.7 - Add and subtract within 1000, 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. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds. |
CCSS.Math.Content.2.NBT.B.8 - Mentally add 10 or 100 to a given number 100-900, and mentally subtract 10 or 100 from a given number 100-900. |
CCSS.Math.Content.2.NBT.B.9 - Explain why addition and subtraction strategies work, using place value and the properties of operations. |
CCSS.Math.Content.3.NBT.A.2 - Fluently add and subtract within 1000 using strategies and algorithms based on place value, properties of operations, and/or the relationships between addition and subtraction. |
Students will be able to use a variety of number-sense based strategies to mentally solve subtraction problems.
Students will use writing to reflect on the effectiveness and efficiency of each strategy used.
• Building Blocks of Math series, specifically Subtraction
• Subtraction Strategy Spotlights PowerPoint Presentation
• Subtraction Strategy Spotlights Note-Taking Guide (1 per student)
• Optional Assessment: Subtraction Strategy Spotlights Mini Quiz (1 per student)
• Optional: Manipulatives (counters, beads, tokens, base ten blocks etc.)
• Optional: Blank tens frames
• Optional: Blank number lines
For additional support, allow students to use manipulatives, blank tens frames, and/or blank number lines to help make the subtraction strategies more concrete and therefore easier to understand. Students can physically move manipulatives or draw jumps on number lines to demonstrate subtraction.
• Counting Back
• Finding Tens
• Number Lines
• Near Doubles
These procedures are general and can be applied to each strategy spotlighted in this activity.
Optional: After students have had exposure to and practice using all four strategies highlighted in this activity, consider using the optional mini quiz as a form of assessment. Here, students are provided four subtraction problems and asked to solve them using whatever strategies they would like. In addition, students must justify why they chose the strategies they did.