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📐
Mathematics
Fractions — Adding Unlike Denominators
Medium
📸 Uploaded Mistake
Student's Written Answer
1/3 + 1/4 = 2/7
P4 Mathematics Worksheet — Question 5
// QUESTION IDENTIFIED BY AI
What is 1/3 + 1/4?
⚠️
What Went Wrong
The student added both numerators and denominators separately (1+1=2, 3+4=7). This is incorrect because fractions must have a common denominator before adding. You cannot simply add the top and bottom numbers independently.
🔑 Key Concepts
Lowest Common Multiple (LCM)
Equivalent Fractions
Common Denominator
Adding Fractions
📝 Step-by-Step Solution
Step 1
Find the Lowest Common Multiple (LCM) of the denominators 3 and 4. The LCM of 3 and 4 is 12.
💡 List multiples: 3, 6, 9, 12… and 4, 8, 12… The smallest common multiple is 12.
Step 2
Convert 1/3 to an equivalent fraction with denominator 12. Multiply both numerator and denominator by 4: 1/3 = 4/12.
💡 Whatever you do to the bottom, you must do to the top to keep the fraction equal.
Step 3
Convert 1/4 to an equivalent fraction with denominator 12. Multiply both numerator and denominator by 3: 1/4 = 3/12.
Step 4
Now add the fractions with the same denominator: 4/12 + 3/12 = 7/12. The denominator stays the same — only add the numerators.
💡 7/12 is already in its simplest form since 7 is a prime number.
✓ Correct Answer:
7/12
🎯 Practice Questions
Easy
What is 1/2 + 1/4?
Hint: One denominator is already a multiple of the other.
Medium
What is 2/5 + 1/3?
Hint: Find the LCM of 5 and 3 first.
Hard
What is 3/8 + 5/6?
Hint: The LCM of 8 and 6 is 24. Don't forget to simplify!
🏛️ MOE Assessment Benchmark
P4 Mathematics
Standard Difficulty
PSLE-Relevant
Adding unlike fractions is a core P4 topic under the Singapore MOE Mathematics syllabus. Students must master finding common denominators before progressing to mixed numbers and fraction multiplication in P5.
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