Some numbers face a certain way, and it is easy to write them backward: 2, 3, 5, 7 and 9. Almost every child does it sometimes. Here is how to check.
- 3 and 5: their round parts bulge to the right.
- 2 and 7: the top goes across to the right, then slants back down to the left.
- 9: the circle is on the left, the line on the right.
Key idea
Curves of 2, 3 and 5 bulge to the right; 9 has its circle on the left.
Why it works
A backward number can still be read, but it slows the reader down, and in math it can be mistaken for a different number.
Worked example: Fix it
Hana wrote 9 with the circle on the right. What should she do?
- A 9 has its circle on the left.
- Start the circle at the top and go left, around, and back up.
- Then pull the line down on the right side of the circle.
Answer: Circle on the left, line on the right.
Common mistake
Writing 3, 5, 7 or 9 backward. Look at a number line or a clock and compare.
For the grown-up. Reversed numbers are common at first and usually fade with practice. Starting each number at its green dot (Writing 5 to 9) prevents most flips.