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A primary use of whole numbers is to keep count of how many objects there are in a collection. Sometimes we're only interested in the approximate number of objects in the collection rather than the precise number. For example, there are approximately 20 symbols in the collection below.
The precise number of symbols in the above collection is 18.
When we think of a collection as occurring in groups of tens, we say we're rounding to the nearest ten . When we think of a collection as occurring in groups of hundreds, we say we're rounding to the nearest hundred . This idea of rounding continues through thousands, ten thousands, hundred thousands, millions, etc.
The process of rounding whole numbers is illustrated in the following examples.
Round 67 to the nearest ten.
On the number line, 67 is more than halfway from 60 to 70. The digit immediately to the right of the tens digit, the round-off digit, is the indicator for this.
Thus, 67, rounded to the nearest ten, is 70.
Round 4,329 to the nearest hundred.
On the number line, 4,329 is less than halfway from 4,300 to 4,400. The digit to the immediate right of the hundreds digit, the round-off digit, is the indicator.
Thus, 4,329, rounded to the nearest hundred is 4,300.
Round 16,500 to the nearest thousand.
On the number line, 16,500 is exactly halfway from 16,000 to 17,000.
By convention, when the number to be rounded is exactly halfway between two numbers, it is rounded to the higher number.
Thus, 16,500, rounded to the nearest thousand, is 17,000.
A person whose salary is $41,450 per year might tell a friend that she makes $41,000 per year. She has rounded 41,450 to the nearest thousand. The number 41,450 is closer to 41,000 than it is to 42,000.
From the observations made in the preceding examples, we can use the following method to round a whole number to a particular position.
Use the method of rounding whole numbers to solve the following problems.
Round 3,426 to the nearest ten.
Thus, 3,426 rounded to the nearest ten is 3,430.
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