Ratios are one of the most heavily tested topics in PSLE Mathematics. They show up in bar model problems, fraction conversions, three-term ratio questions, and multi-step word problems.

The frustrating part? Students who understand ratios still lose marks — not because they can’t do the math, but because they fall into the same traps over and over.

Here are the 8 most common ratio mistakes we see P6 students make, with the exact fix for each one.

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Mistake 1: Writing the Ratio in the Wrong Order

This is the #1 ratio error. It costs zero thinking effort to avoid, yet students lose full marks for it every year.

The Fix: Always write the labels first (e.g., “Boys : Girls = ”), then fill in the numbers. Never jump straight to numbers.

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Mistake 2: Forgetting to Simplify

Many students write a correct ratio but forget to express it in simplest form — and lose a mark.

The Fix: After writing any ratio, ask yourself: “Can I divide all terms by the same number?” If the question says “simplest form,” you must simplify or you will lose marks.

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Mistake 3: Mixing Up Part-to-Part and Part-to-Whole

This mistake is especially common when the question asks for a ratio involving the total.

The Fix: Circle the word “total” whenever you see it in a ratio question. Total means you need to add all parts first before writing the ratio.

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Mistake 4: Wrong LCM When Combining Two Ratios

Combining two ratios into a three-term ratio is one of the hardest P6 ratio skills. The most common mistake? Making the wrong term equal.

The Fix: Write the common term’s values from each ratio side by side and find their LCM. Never skip this step — even if one already divides the other.

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Mistake 5: Fraction-to-Ratio Conversion Errors

Fraction-ratio conversion catches even strong students. The wording is tricky.

The Fix: Ask yourself: ”$\frac{2}{5}$ of what?” If it’s $\frac{2}{5}$ of another person, the ratio is numerator : denominator. If it’s $\frac{2}{5}$ of the total, subtract to find the other part.

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Mistake 6: Total vs Difference Mix-Up in Word Problems

This is the classic “1 unit = ?” mistake that turns a 4-mark question into zero marks.

Keyword in Question	What It Tells You	Formula
”altogether,” “total,” “in all”	Total given	1 unit = Total ÷ sum of ratio parts
”more than,” “fewer than,” “difference”	Difference given	1 unit = Difference ÷ difference of ratio parts

The Fix: Before dividing, highlight the keyword. “Total” → add the ratio parts. “More/fewer” → subtract the ratio parts. Getting this one right is worth 3-4 marks every time.

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Mistake 7: Forgetting to Convert Units Before Writing Ratios

When quantities are in different units, you must convert first — otherwise the ratio is meaningless.

The Fix: Before writing any ratio, check: “Are both quantities in the same unit?” If not, convert the larger unit to the smaller one (it keeps everything as whole numbers).

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Mistake 8: Not Answering What the Question Asks

This is technically not a ratio-specific error — but it costs more marks on ratio questions than any other topic because ratio word problems are multi-step.

The Fix: After solving, re-read the question’s last line before writing your answer. Ask: “Did I answer exactly what was asked — total, difference, one person’s share, or the ratio?”

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Quick-Reference: The 8 Mistakes at a Glance

#	Mistake	Quick Fix
1	Wrong ratio order	Write labels first, then numbers
2	Didn’t simplify	Always check for common factors
3	Part-to-part vs part-to-whole	Circle “total” — add parts first
4	Wrong LCM when combining	Identify common term, find LCM
5	Fraction-to-ratio error	Ask: ”$\frac{a}{b}$ of what?“
6	Total vs difference mix-up	Highlight “altogether” or “more than”
7	Different units	Convert to same unit before writing
8	Not answering the question	Re-read the last line before writing your answer

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The 30-Second Pre-Check

Before you submit any ratio answer, run through this checklist:

This takes 30 seconds and can save you 10-20 marks across an entire PSLE paper.

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