Topic F Extending Addition to 100 The final topic of the year provides more practice with adding 2 two-digit numbers, this time with larger totals. Students apply their place value understanding and knowledge of Level 3 strategies to add pairs of two-digit numbers that have sums within 100. Like in module 5, students explore three primary ways to solve problems. They add like units (tens with tens and ones with ones), add tens first, and make the next ten. Based on their prior experience with these ways of decomposing and composing, students are now more likely to examine the structure of the addends in a problem and strategically select a way to solve it. In this topic, students continue to • solve problems in more than one way and compare the solution pathways, • reason about common errors in written methods, and • determine the equality of various expressions that are used to make easier problems. Students come to this topic understanding that when they add, it is sometimes useful to compose a ten. In preparation for working with larger numbers in grade 2, these lessons present the idea that it is possible to compose 1 hundred when there are 10 tens. Students relate their knowledge of partners to 10 to working with multiples of 10 to make 100, and they apply the different ways they know to add 2 two-digit numbers. Students end the grade 1 year well equipped to approach addition problems in grade 2 with a variety of flexible and efficient strategies.
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