Place value- Rounding decimal numbers on the calculator

I can round decimal numbers on the calculator.

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Students learn to round decimal numbers on the calculator to the tenths, hundredths, and thousandths place.

Discuss with students that it is important to be able to round to the tenths, hundredths, and thousandths on the calculator, so that they don't need to write all the numbers in the decimal places down. This is useful, for example, with division.

The interactive whiteboard has a number of true/false statements about rounding numbers. Students must decide if they are true or false and show thumbs up or thumbs down. You can erase the grey boxes to show the answer. Ask students how they determined their answers and what they need to pay attention to when rounding to tenths and hundredths.

Explain that you can round a decimal number to the tenths, hundredths, and thousandths place. When you round to the tenths place, you look at the number in the hundredths place (2nd digit after the decimal point). When rounding to the hundredths place, you look at the number in the thousandths place(3rd digit after the decimal point). When rounding to the thousandths place, you look at the number that is fourth after the decimal point (it's called the ten thousandths place). If the number is 4 or less, you round down. If the number is 5 or greater, you round up and add 1 to the prior number.

To check that students understand rounding decimal numbers on the calculator, you can ask the following questions:

- Which number do you look at when you want to round a decimal number to the tenths/hundredths/thousandths place?

- What do you do when the number is a 5?

- What happens to the number in the tenths/hundredths/thousandths place if the number is a 5?

Students first round a number to the tenths or hundredths place, with the calculator showing a number with 7 decimal places. Next the students must round a number with 6 decimal places to the thousandths place. Ask students how they ave rounded the number and see which number they use to determine if they round up or down.

Repeat the goal and ask why it is important to be able to round decimal numbers. You also use rounding when you do approximate calculations in the future. Ask which numbers to look at when you want to round a number. When rounding to the tenths place, you look at the hundredths, when rounding to the hundredths, you look at the thousandths, and when rounding to the thousandths, you look at the fourth number, the ten thousandths. To check this the interactive whiteboard has a few calculators and students must round to the tenths, hundredths and thousandths place. Finally students must decide if a number should be rounded up or down, and stand up or down.

Students who have difficulty with this goal should start with rounding to whole numbers, to tenths, and to hundredths with decimal numbers with a maximum of 3 decimal places.

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