Reading Decimal Fractions

Background

Students’ early contact with a decimal point is often in the context of money. Using money is not reliant on fraction knowledge. Students can come to think of the decimal point as separating two whole numbers, the dollars and the cents. So students with no experience of decimal fractions

can often solve money problems like $1.50 + $2.50 = $4.00. This demonstrates that the use of the decimal point in money is not the same as its use in measurements like 4.567 metres.

Activity

Check that the students can name the value of each digit in numbers up to 999 999 999 999.

Provide copies of the decimal fraction mat enlarged to A3 size. Get the students to cut out a large piece (one-tenth) and place it on an uncut mat. Discuss how big the piece is compared to the whole mat (one-tenth the size). Get the students to cut out the next largest piece and place it on an uncut mat. Discuss the size of this piece compared to the whole (one-hundredth). Continue this process to progressively smaller pieces (one-thousandth and one ten-thousandth). Get the students to try to cut a ten-thousandth into 10 equal pieces. Discuss the size of each of these tiny

pieces compared to the original mat (one hundred-thousandth). Discuss how continued cutting would produce millionths to hundred-billionths. Emphasise that, with each division by 10, the pieces decrease in relative size very rapidly.

Get the students to draw a large table with headings Ones, Tenths, Hundredths, Thousandths, and Ten-thousandths. Use a whiteboard or chalk on the carpet.

Ones Tenths Hundredths Thousandths Ten-thousandths

Get the students to cut out the matching decimal mat model and place the pieces in the correct column of the table.