How do you round decimal numbers?


Quick Answer

Round a decimal to a specific place by looking at the digit to the immediate right. If that digit's value is less than five, the place value remains the same, but if it is five or greater, the place value increases by one. Digits to the right are then dropped.

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Full Answer

If the place you have chosen to round to has a value of nine and must be rounded up, it becomes a zero, and the value of the preceding digit increases by one. For instance, 1.795 rounded to the nearest hundredth becomes 1.80; additionally, 1.9995 rounded to the nearest thousandth becomes 2.000.

When rounding a decimal to the right of the decimal point, no zeros need to be added; for instance, 123.456 rounded to the nearest tenth becomes 123.5. However, when rounding to the left of the decimal point, zeros must be used as placeholders for any digits dropped by rounding on the left side of the decimal; for examples, 12345.6 rounded to the nearest hundred becomes 12300.

Places are named by counting to the left or right of the "units" place, just to the left of the decimal. Every place away from the units place is one power of ten larger or smaller (units, tens, hundreds, thousands, ten-thousands, etc.). If a "th" ends the place name, then it is counting to the right of the units place, instead of left. Thus, the hundredths place is easily found by counting to the right of the units place (units --> tenths --> hundredths), while the hundreds place is found by counting to the left of the units place (hundreds <-- tens <-- units).

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