Look at the two labelled numbers and count the equal spaces between them. The gap shared by the number of spaces tells you what one space is worth. From 0 to 1 in 10 spaces, each space is 0.1 (one tenth). From 0.3 to 0.4 in 10 spaces, each is 0.01 (one hundredth). Then count the spaces from the start to the arrow.
Explore this idea with maths tools
Equal parts, equal wholes
2/4 = 4/8
Both bars are the same length. Find a division of the second bar that lines up exactly with the coloured edge.
Words to know
- tenth
- one of 10 equal parts of one, written 0.1
- hundredth
- one of 100 equal parts of one, written 0.01
- scale
- how much each space on a line is worth
Worked examples
0 to 1 has 10 equal spaces. The arrow is 7 spaces after 0. What decimal is it?
- 1.Each space is 0.1.
- 2.7 tenths is 0.7.
= 0.7
0.3 to 0.4 has 10 equal spaces. The arrow is 6 spaces after 0.3. What decimal is it?
- 1.The gap of 0.1 shared into 10 spaces makes each space 0.01.
- 2.0.3 + 6 hundredths = 0.36.
= 0.36
2 to 3 has 4 equal spaces. The arrow is 3 spaces after 2. What number is it?
- 1.1 ÷ 4 = 0.25, so each space is 0.25.
- 2.3 × 0.25 = 0.75, and 2 + 0.75 = 2.75.
= 2.75
For parents
Method: Find the size of one space
What to say: What is the gap between the labels? How many spaces share it?
Common mistakes:
- Reads the number of tenths as a whole number, leaving out the decimal point (7 for 0.7).
- Assumes each small space is one hundredth without checking the scale.
- Assumes each space is one tenth without checking the scale.
- Writes 'three tenths and six hundredths' as 0.306, putting the hundredths after an extra zero.
- Reads only the decimal part and drops the whole number (3.7 read as 0.7).
- Counts the starting mark as a jump, so the reading is one space too far.