Fractions
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These principles are fundamental in arithmetic and are widely used in various mathematical operations.
Basic Mathematical Principles
1. Sign Rules for Multiplication/Division
Operation | Example |
---|---|
(+) × (+) = + | 3 × 4 = 12 |
(+) × (-) = – | 3 × (-4) = -12 |
(-) × (+) = – | -3 × 4 = -12 |
(-) × (-) = + | -3 × (-4) = 12 |
(+) ÷ (+) = + | 12 ÷ 3 = 4 |
(+) ÷ (-) = – | 12 ÷ (-3) = -4 |
(-) ÷ (+) = – | -12 ÷ 3 = -4 |
(-) ÷ (-) = + | -12 ÷ (-3) = 4 |
2. Finding Common Factors
Example: Common factors of 12 and 8
- Factors of 12: 1, 2, 3, 4, 6, 12
- Factors of 8: 1, 2, 4, 8
- Common factors: 2 and 4
3. Lowest Common Denominator (LCD)
Example: LCD of 6 and 4
- Multiples of 6: 6, 12, 18, 24…
- Multiples of 4: 4, 8, 12, 16…
- Smallest common multiple: 12
4. Fraction Equivalence
1⁄2 = 3×1⁄3×2 = 3⁄6
4⁄10 = 2×2⁄2×5 = 2⁄5
5. Converting Mixed Numbers
Example: 12⁄3
= (1×3) + 2⁄3 = 5⁄3
Let’s break down the content with examples for each principle:
- Sign of answer when multiplying or dividing:
- Multiplication:
- +×+=++×+=+: 3×4=123×4=12
- +×−=−+×−=−: 3×(−4)=−123×(−4)=−12
- −×+=−−×+=−: −3×4=−12−3×4=−12
- −×−=+−×−=+: −3×(−4)=12−3×(−4)=12
- Division:
- +÷+=++÷+=+: 12÷3=412÷3=4
- +÷−=−+÷−=−: 12÷(−3)=−412÷(−3)=−4
- −÷+=−−÷+=−: −12÷3=−4−12÷3=−4
- −÷−=+−÷−=+: −12÷(−3)=4−12÷(−3)=4
- Multiplication:
- Finding common factors:
- Common factors of 12 and 8 are numbers that divide both 12 and 8 without leaving a remainder.
- Factors of 12: 1, 2, 3, 4, 6, 12
- Factors of 8: 1, 2, 4, 8
- Common factors: 2 and 4
- Common factors of 12 and 8 are numbers that divide both 12 and 8 without leaving a remainder.
- Finding the lowest common denominator (LCD) when adding and subtracting fractions:
- To add or subtract fractions, they must have the same denominator. The LCD is the smallest number that both denominators divide into evenly.
- For fractions with denominators 6 and 4:
- Multiples of 6: 6, 12, 18, 24, …
- Multiples of 4: 4, 8, 12, 16, 20, …
- LCD is 12.
- For fractions with denominators 6 and 4:
- To add or subtract fractions, they must have the same denominator. The LCD is the smallest number that both denominators divide into evenly.
- The value of a fraction is not changed if the top and bottom are multiplied or divided by the same number:
- Multiplying numerator and denominator by the same number:
- 12=3×13×2=3621=3×23×1=63
- Dividing numerator and denominator by the same number:
- 410=2×22×5=25104=2×52×2=52
- Multiplying numerator and denominator by the same number:
- Converting mixed numbers to fractions:
- A mixed number consists of a whole number and a fraction. To convert it to an improper fraction:
- Multiply the whole number by the denominator and add the numerator.
- Example: 123=(1×3)+23=53132=3(1×3)+2=35
- A mixed number consists of a whole number and a fraction. To convert it to an improper fraction:
Operations Order
Now, Let go deeper into Understanding Fraction Equivalence
Order of Operations (BIDMAS)
The order of operations is a set of rules that ensures everyone solves mathematical expressions the same way. The mnemonic BIDMAS helps you remember the correct order:
- B – Brackets
- I – Indices (powers and roots)
- DM – Division and Multiplication (left to right)
- AS – Addition and Subtraction (left to right)
Example 1: Sally and Rola’s Cakes
Sally and Rola are twins. Their friends give them identical cakes for their birthday. Sally eats 1/8 of her cake, and Rola eats 1/6 of her cake. How much cake is left?
Solution: Use BIDMAS to calculate the remaining cake for each twin and then add the results.
Example 2: Equipment Replacement Part
A part has broken on a machine and needs to be replaced. The replacement part must be between 8 1/7 cm and 6 1/7 cm long to fit. The diagram shows the replacement part. Will this part fit the machine? Explain your answer.
Solution: Compare the length of the replacement part with the given range using BIDMAS to simplify the fractions.

Practice Exercises
Try solving these problems using the BIDMAS rules:
- Calculate: 3 + 4 × 2
- Simplify: (5 + 3) × (6 – 2)
- Evaluate: 10 ÷ 2 + 5 × 3
- Solve: 12 – (4 + 2) × 2
- Determine: 8 ÷ 2 × (2 + 2)
- Calculate: 20 ÷ 4 + 7 × 2
- Simplify: (9 – 3) × (4 + 2)
- Evaluate: 15 ÷ 3 + 4 × 5
- Solve: 18 – (3 + 2) × 2
- Determine: 24 ÷ (6 – 2) × 3
Answers:
- 3 + 4 × 2 = 11 (Multiplication first: 4 × 2 = 8, then 3 + 8 = 11)
- (5 + 3) × (6 – 2) = 32 (Brackets first: 5 + 3 = 8 and 6 – 2 = 4, then 8 × 4 = 32)
- 10 ÷ 2 + 5 × 3 = 20 (Division and multiplication first: 10 ÷ 2 = 5 and 5 × 3 = 15, then 5 + 15 = 20)
- 12 – (4 + 2) × 2 = 0 (Brackets first: 4 + 2 = 6, then 6 × 2 = 12, then 12 – 12 = 0)
- 8 ÷ 2 × (2 + 2) = 16 (Brackets first: 2 + 2 = 4, then division and multiplication left to right: 8 ÷ 2 = 4, then 4 × 4 = 16)
- 20 ÷ 4 + 7 × 2 = 19 (Division and multiplication first: 20 ÷ 4 = 5 and 7 × 2 = 14, then 5 + 14 = 19)
- (9 – 3) × (4 + 2) = 36 (Brackets first: 9 – 3 = 6 and 4 + 2 = 6, then 6 × 6 = 36)
- 15 ÷ 3 + 4 × 5 = 25 (Division and multiplication first: 15 ÷ 3 = 5 and 4 × 5 = 20, then 5 + 20 = 25)
- 18 – (3 + 2) × 2 = 8 (Brackets first: 3 + 2 = 5, then 5 × 2 = 10, then 18 – 10 = 8)
- 24 ÷ (6 – 2) × 3 = 18 (Brackets first: 6 – 2 = 4, then division and multiplication left to right: 24 ÷ 4 = 6, then 6 × 3 = 18)