Rounding Numbers : Rounding Numbers (creating estimates)
in the 4th grade
What does it mean to “round” a number? : What does it mean to “round” a number? Rounding a number means to change an exact value into an estimate. We can use estimates when we don’t need an exact answer. For example, pretend that a student earned $254.72 doing chores. What if someone asked the student, “How much have you earned?” The student might answer, “Oh, I’ve earned about $255.” The student’s answer is an estimate of the exact amount. In the answer above, the student rounded 72 cents up to 1 whole dollar. The ROUNDING RULES work like this… = about $1.00
The Rounding Rules – Rule 1 : The Rounding Rules – Rule 1 $254.72 First, locate the place value where the estimation will happen. In this example, the student rounded to the ONES place. $254.72 ? But if this digit belongs to the high-number group, then the estimated place value does change. It increases by 1. Look at the exact number again: $254.72 Now ask yourself:
Q. Does the “7” belong to the low-number or high-number group?
Q. Will the “7” cause the “4” to stay the same, or to increase? Now look at the digit to the right and apply the following rule…
?Rule 1:
? If this digit belongs to the low-number group, then the estimated place value doesn’t change.
The Rounding Rules – Rule 2 : The Rounding Rules – Rule 2 Answer: the “7” in the number $254.72 belongs to the high-number group, so it does cause the “4” to increase to “5.” Therefore, when the exact value of $254.72 is rounded to the ONES place, it changes to the estimate of $255.00 Are you wondering why the .72 was replaced with .00 ?? $2 5 4 . 7 2 5 The 72 cents were rounded off in the process of changing the exact value to an estimate. ?Rule 2: 7 2 0 0 after rounding, all of the digits to the right of the estimated place value turn into zeros. The important point to remember is this:
More examples of Rounding Numbers(creating estimated numbers) : More examples of Rounding Numbers(creating estimated numbers) Round 25,678,271 to the thousands place. 2 5 , 6 7 8 , 2 7 1 2 5 , 6 7 8 , 2 7 1 2 5 , 6 7 , 0 0 0 Round 99,070,861 to the hundreds place. 9 9 , 0 7 0 , 8 6 1 9 9 , 0 7 0 , 8 6 1 9 9 , 0 7 0 , 0 0 9 8 The 2 belongs to the low-number group.
So the 8 doesn’t change. The 6 belongs to the high-number group.
So the 8 increases to 9.
More examples of Rounding Numbers(creating estimated numbers) : 0 0 More examples of Rounding Numbers(creating estimated numbers) Round 98,070,561 to the ten millions place. 9 8 , 0 7 0 , 5 6 1 9 8 , 0 7 0 , 5 6 1 1 0 0 , 0 0 0 , 0 0 0 The 8 belongs to the high-number group.
So the 9 increases to 10. Round $12,345.98 to the ones place. $1 2 , 3 4 5 . 9 8 $1 2 , 3 4 5 . 9 8 The 9 belongs to the high-number group.
So the 5 increases to 6. $1 2 , 3 4 6 .