This unit builds upon students' work with place value within 20, now focusing on the role of place value in
the addition and subtraction of numbers to 40. Students study, organize, and manipulate numbers within 40. Students use fingers, linking cubes, dimes, and pennies to represent numbers to 40 in various ways—from all
ones to tens and ones. They use a place value chart to organize units.
Students also compare quantities and begin using the symbols for greater than (>) and less than (<). Students demonstrate their understanding of place value when they recognize that 18 is less than 21 since 2 tens already have a greater value than 1 ten 8 ones.
Students also focus on on addition and subtraction of tens. Having used concrete models at the beginning of the unit to represent 10 more and 10 less, students now recognize that just as 3 + 1 = 4, 3 tens + 1 ten = 4 tens.With this understanding, students add and subtract a multiple of 10 from another multiple of 10.
Finally, students use familiar strategies to add two-digit and single-digit numbers within 40. Students apply strategy of counting on and use the strategy of making ten, this time making the next ten. For instance, when adding 28 + 5, students break 5 into 2 and 3 so that 28 and 2 can make the next ten, which is 30, or 3 tens, and then add 3 to make 33.
Students also compare quantities and begin using the symbols for greater than (>) and less than (<). Students demonstrate their understanding of place value when they recognize that 18 is less than 21 since 2 tens already have a greater value than 1 ten 8 ones.
Students also focus on on addition and subtraction of tens. Having used concrete models at the beginning of the unit to represent 10 more and 10 less, students now recognize that just as 3 + 1 = 4, 3 tens + 1 ten = 4 tens.With this understanding, students add and subtract a multiple of 10 from another multiple of 10.
Finally, students use familiar strategies to add two-digit and single-digit numbers within 40. Students apply strategy of counting on and use the strategy of making ten, this time making the next ten. For instance, when adding 28 + 5, students break 5 into 2 and 3 so that 28 and 2 can make the next ten, which is 30, or 3 tens, and then add 3 to make 33.
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