Rounding Decimals

In the United States, gasoline prices are usually written with the decimal part as thousandths of a dollar. For example, a gas station might post the price of unleaded gas at $\$3.279$ per gallon. But if you were to buy exactly one gallon of gas at this price, you would pay $3.28 , because the final price would be rounded to the nearest cent. In Whole Numbers, we saw that we round numbers to get an approximate value when the exact value is not needed. Suppose we wanted to round $2.72 to the nearest dollar. Is it closer to $2 or to $3? What if we wanted to round $2.72 to the nearest ten cents; is it closer to $2.70 or to $2.80? The number lines in the image below can help us answer those questions.

example

Round $18.379$ to the nearest hundredth. Solution

$18.379$
Locate the hundredths place and mark it with an arrow.
Underline the digit to the right of the $7$.
Because $9$ is greater than or equal to $5$, add $1$ to the $7$.
Rewrite the number, deleting all digits to the right of the hundredths place.	$18.38$
$18.38 is 18.379$ rounded to the nearest hundredth.

example

Round $18.379$ to the nearest ⓐ tenth ⓑ whole number.

Answer: Solution

ⓐ Round $18.379$ to the nearest tenth.
$18.379$
Locate the tenths place and mark it with an arrow.
Underline the digit to the right of the tenths digit.
Because $7$ is greater than or equal to $5$, add $1$ to the $3$.
Rewrite the number, deleting all digits to the right of the tenths place.	$18.4$
So, $18.379$ rounded to the nearest tenth is $18.4$.

ⓑ Round $18.379$ to the nearest whole number.
$18.379$
Locate the ones place and mark it with an arrow.
Underline the digit to the right of the ones place.
Since $3$ is not greater than or equal to $5$, do not add $1$ to the $8$.
Rewrite the number, deleting all digits to the right of the ones place.	$18$
So $18.379$ rounded to the nearest whole number is $18$.

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