Ratio questions: stopping at one unit
On the script you see "2 units = 24, 1 unit = 12" and then 12 written as the final answer. Finding 1 unit is the key step, but the question asked for something else, such as the total or one person's share. The method is right and the answer mark is lost.
What it looks like
The ratio of the number of stickers Mei has to the number Ravi has is 3 : 5. Ravi has 24 more stickers than Mei. How many stickers do they have altogether?
- Difference: 5 units − 3 units = 2 units
- 2 units = 24, so 1 unit = 24 ÷ 2 = 12
- Altogether: 3 units + 5 units = 8 units
- 8 units = 8 × 12 = 96
Why 12 stickers is wrong: The value of 1 unit was given as the answer, instead of multiplying it by the 8 units for the total.
Why children do it
- Finding 1 unit feels like the solution because it is the step that takes the most thinking.
- Children do not go back to check which quantity the question asked for: one person, the difference, or the total.
- Units are abstract, so a child may not notice that 12 stickers is far too few for two children together.
How to fix it at home
- Ask your child to label the bar model with what the question wants, such as "? altogether", before working.
- Have your child write "the question asks for ___ units" before finding 1 unit.
- Check the answer against the story: Ravi alone has 5 × 12 = 60 stickers, so 12 cannot be the total.
- Practise questions that ask for different things from the same ratio: one share, the difference, the total.
Questions parents ask
Why does the unit method work so well for ratio?
It turns every ratio question into the same two steps: find 1 unit, then multiply by the units you need. The second step is the one children skip.
How do I know when the habit is gone?
Knowbotic counts a habit as fixed after your child gets 3 questions of that type right in a row, so you can see when it stops costing marks.
Other careless mistakes
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