GuideMath · P5 / P6Problem Sums
Constant Difference / Constant Total Guide
When both quantities change by the same amount, the DIFFERENCE stays the same. When one gains what the other loses, the TOTAL stays the same.
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1
Constant Difference
Both people gain or lose the same amount. The gap between them never changes.
2
Constant Total
One person's gain equals another person's loss. The total never changes.
3
How to Spot It
Ask: is money moving between them (constant total) or is each getting/losing separately (constant difference)?
⚠️ Common Mistakes
Don't fall into these traps
- ✕Assuming the total is constant when it isn't
- ✕Using the wrong 'before' ratio for the difference
- ✕Skipping the check-in question
Teacher Hidayah's Tip
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Write 'DIFFERENCE stays' or 'TOTAL stays' at the top of your working before drawing bars.
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Sample Question
Try it, then read the worked solution
Question
Amy and Bala each save $5 more per week. If the ratio was 3 : 5 and later becomes 2 : 3, find their original amounts.
Worked Solution
- 1Difference is constant (both gain $5, gap unchanged)
- 2Before: 5u − 3u = 2u ; After: 3p − 2p = 1p
- 3So 2u = 1p → use to solve for original amounts
Everything for Problem Sums
Each topic in the library comes with the full 5-piece bundle.
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Before-Class Prep
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After-Class Practice
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Downloadable Notes
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One-Page Mind Map
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Mistake Fix Zone