In Topic C, students pick up from their previous work with 10 more and 10 less to extend the concept to adding and subtracting multiples of 10. In Lesson 11, students represent the addition of ten more with concrete objects and number bonds, first using the numeral and then writing as units of ten, as shown. After creating such number bonds for several examples, students notice that only the unit has changed (e.g., 3 bananas + 1 banana = 4 bananas, just as 3 tens + 1 ten = 4 tens). As students explore, they see that this relationship is present even when adding more than 1 ten. They come to realize that 2 tens + 2 tens = 4 tens, just as 2 + 2 = 4 (1.NBT.4). Students also explore this relationship with subtraction, seeing that 4 tens can be decomposed as 3 tens and 1 ten, and that 4 tens – 3 tens = 1 ten, just as 4 – 3 = 1 (1.NBT.6). Students see that the arrow is used to show the addition or subtraction of an amount, regardless of whether the number is increasing (adding) or decreasing (subtracting). This provides an important foundation for applying strategies such as the make ten strategy, described in Topic D. In Lesson 12, students add multiples of 10 to two-digit numbers that include both tens and ones. They recognize that when tens are added to a number, the ones remain the same. Students use the cubes within their kit of 4 ten-sticks as well as the more abstract manipulatives of dimes and pennies, to explore the concept. They represent their computation in familiar ways such as number bonds, quick ten drawings, arrow notation, and by using the place value chart to organize the quantities as tens and ones.

## Grade 1 Mathematics Module 4, Topic C

## Downloadable Resources

## Common Core Learning Standards

CCLS | State Standard |
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1.NBT.2 | Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand... |

1.NBT.4 | Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit... |

1.NBT.6 | Subtract multiples of 10 in the range 10-90 from multiples of 10 in the range 10-90 (positive or... |