Flexibility in thinking about numbers is critical (e.g., 84 is equivalent to 8 tens and 4 ones, or 7 tens and 14 ones, or 5 tens and 34 ones, etc.). This flexibility builds background understanding for the ideas used when regrouping. When subtracting 18 from 174, a student may choose to regroup and think of 174 as 1 hundred, 6 tens, and 14 ones.
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Number lines are useful tools when developing a conceptual understanding of rounding with whole numbers. When given a number to round, locate it on the number line. Next, determine the closest multiples of thousand, ten-thousand, or hundred-thousand it is between. Then, identify to which it is closer.
Identify the range of numbers that round to a given thousand, ten thousand, and hundred thousand. (c)
Group a collection of up to 110 objects into sets of tens and ones. (a)
Computational fluency is the ability to think flexibly in order to choose appropriate strategies to solve problems accurately and efficiently.
Quickly recognizing and naming the number of objects in a small group without counting is called subitizing. The size of the group a student can subitize is dependent upon the arrangement of the dots or objects. At this age, students should subitize regular arrangements up to 5.