# Addition and Subtraction Within 100 *A Grade 2 Mathematics lesson on two-digit numbers* ## Slide 1: Addition and Subtraction Within 100 ![Addition and Subtraction Within 100](https://goa-cc-uat-aili-app-001.azurewebsites.net/api/generate/4c0ef14a-f2a7-420a-bf4c-d25555cc07b0/asset/2016) *A Grade 2 math adventure with numbers up to 100* > Notes: Learning intention: We are learning to add and subtract two-digit numbers up to 100. Success criteria: I can add two-digit numbers. I can subtract two-digit numbers. I can check my answer. Materials: base ten blocks, hundred chart, whiteboards. Time: 3 minutes for intro and hook. ## Slide 2: What We Will Learn Today - We add numbers up to 100 ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29844)). - We subtract numbers up to 100 ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29844)). - The order in which more than two numbers are added does not affect the sum([Details](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846)). - We understand the associative property of addition([Details](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846)). *Sources: [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29844), [Details](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846)* > Notes: Learning intention: understand today's goal. Success criteria: I can say what addition and subtraction mean. Time: 4 minutes. Formative checkpoint: thumbs up if you know what 'sum' and 'difference' mean. Support: review vocabulary with picture cards. Extension: ask students to give an example sentence using each word. ## Slide 3: Ways to Add Two-Digit Numbers 1. **Make a ten**: Break apart a number to build a group of ten first ([Details](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846)). 2. **Use doubles**: Use a known double, like 20+20, to help solve a new problem ([Details](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846)). 3. **Add tens, then ones**: Add the tens together, then add the ones together ([Details](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846)). 4. **Check your work**: Use subtraction to check that your sum is correct ([Details](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846)). *Sources: [Details](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846)* > Notes: Learning intention: use strategies for two-digit addition. Success criteria: I can apply the associative property of addition. Materials: addition problems with more than two numbers. Time: 8 minutes. Formative checkpoint: observe students applying the associative property. Support: pair students with a hundred chart. Extension: have students invent their own two-digit addition problem and solve it two ways. ## Slide 4: Addition and Subtraction Are Connected **Addition** Addition puts numbers together to find a sum. We can find a missing number in an addition problem ([Details](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846)). **Subtraction** Subtraction takes one quantity away from another, or compares two quantities, to find a difference; it undoes addition, so 85 - 38 = 47 because 47 + 38 = 85. *Sources: [Details](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846)* > Notes: Learning intention: see addition and subtraction as opposite operations. Success criteria: I can apply the associative property to solve addition problems. Time: 6 minutes. Formative checkpoint: exit slip with addition problems using more than two numbers. Support: use fact family triangle cards. Extension: create a fact family with three-digit numbers as a preview of Grade 3 work. ## Slide 5: Solve It: The Class Bake Sale Our class baked 47 cookies on Monday. We baked 38 more cookies on Tuesday. How many cookies do we have now? Later, we sold 62 cookies. How many cookies are left? Students solve problems using addition and subtraction of countable quantities ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29844)). > Using addition and subtraction to solve a real problem Our class baked 47 cookies on Monday. We baked 38 more cookies on Tuesday. How many cookies do we have now? Later, we sold 62 cookies. How many cookies are left? Students solve problems using addition and subtraction of countable quantities ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29844)). *Sources: [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29844)* > Notes: Learning intention: apply addition and subtraction strategies to a real-world problem. Success criteria: I can solve a two-step problem within 100 and explain my thinking. Materials: whiteboards, base ten blocks, cookie counters or pictures. Time: 10 minutes. Formative checkpoint: walk around and check for a chosen strategy plus a check step. Support: give smaller numbers or a hundred chart. Extension: ask students to write their own bake sale story problem for a partner to solve. ## Slide 6: Great Work, Mathematicians! **Summary:** Today we added and subtracted numbers up to 100 using strategies like making tens, using doubles, and adding tens then ones. Students apply strategies for addition and subtraction within 1000([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29923)). **Question:** Can you think of a strategy you would use to solve 56 + 27, and why? *Sources: [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29844), [Details](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846), [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29923)* > Notes: Learning intention: consolidate today's learning and preview future connections. Success criteria: I can name a strategy I used today. Time: 5 minutes. Formative checkpoint: exit ticket answering the closing question. Support: sentence starter 'I would use ___ because ___.' Extension: challenge students to try the problem with a second strategy to compare answers. --- *AILI presentation · language en · model claude-sonnet-5 · generated 2026-09-17 · id 4c0ef14a-f2a7-420a-bf4c-d25555cc07b0* ### Sources - node:n1: Number: Quantity is measured with numbers that enable counting, labelling, comparing, and operating. (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29733) - node:n2: How can addition and subtraction provide perspectives of number? (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29756) - node:n3: Students examine addition and subtraction within 20. (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29757) - node:n4: Details (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29759) - node:n5: Number: Quantity is measured with numbers that enable counting, labelling, comparing, and operating. (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29820) - node:n6: How can addition and subtraction be interpreted? (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29843) - node:n7: Students investigate addition and subtraction within 100. (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29844) - node:n8: Details (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29846) - node:n9: Number: Quantity is measured with numbers that enable counting, labelling, comparing, and operating. (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29915) - node:n10: How can processes be established for addition and subtraction? (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29922) - node:n11: Students apply strategies for addition and subtraction within 1000. (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29923) - node:n12: Details (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/29925)