Multiplying fractions · Grade 8
In Grade 8 you learn: multiplying mixed numbers.
To multiply fractions, multiply the tops and multiply the bottoms, then simplify. “Of” means multiply, so 1/2 of 3/4 is 3/8. Multiplying by a fraction less than 1 makes a number smaller.
Key facts
- a/b × c/d = (a × c)/(b × d). Simplify at the end, or cancel common factors first.
- A whole number n is n/1: 3/4 × 8 = 24/4 = 6.
- “Of” means multiply: 2/3 of 12 is 2/3 × 12 = 8.
- Change mixed numbers into improper fractions before multiplying or dividing.
Worked examples
Example 1
Work out 1/4 × 12.
Answer: 3
Example 2
Work out 2/3 × 3/5.
Answer: 2/5
Example 3
Work out 2/3 × 9/10.
Answer: 3/5
Example 4
A recipe uses 3/4 of a cup of flour. How much flour is in 2/3 of the recipe?
Answer: 1/2 of a cup
Example 5
Work out 2 1/2 × 1 3/5.
Answer: 4