Example 1: Two proper fractions
Calculate 2/3 × 3/5.
- 1Multiply the numerators: 2 × 3 = 6.
- 2Multiply the denominators: 3 × 5 = 15.
- 3This gives 6/15.
- 4Simplify by dividing both by 3: 2/5.
Answer: 2/5
Multiplying fractions is the easiest of the four fraction operations: multiply the tops, multiply the bottoms, simplify. The difficulty is not the method but unlearning the common denominator habit that adding fractions builds.
a/b × c/d = (a × c) / (b × d)
Multiply the numerators to get the new numerator and the denominators to get the new denominator. No common denominator is needed. Simplifying before multiplying, by cancelling any factor shared between a numerator and a denominator, keeps the numbers small.
Calculate 2/3 × 3/5.
Answer: 2/5
Calculate 4/9 × 3/8.
Answer: 1/6
Calculate 1½ × 2/3.
Answer: 1
Work through these in order. Each answer opens to show the full method, so you can check your reasoning rather than just your final number.
Calculate: 1/2 × 3/4
Answer: 3/8
Multiply tops and bottoms: (1×3)/(2×4) = 3/8.
Calculate: 2/5 × 1/3
Answer: 2/15
(2×1)/(5×3) = 2/15.
Calculate: 3/4 × 4
Answer: 3
Write 4 as 4/1: (3×4)/(4×1) = 12/4 = 3.
Calculate: 1/3 × 1/3
Answer: 1/9
(1×1)/(3×3) = 1/9.
Calculate: 2/3 × 9/10
Answer: 3/5
(2×9)/(3×10) = 18/30, which simplifies by 6 to 3/5.
Calculate: 5/6 × 3/10
Answer: 1/4
Cancel 5 with 10 and 3 with 6: 1/2 × 1/2 = 1/4.
What is 3/4 of 20?
Answer: 15
'Of' means multiply: 3/4 × 20 = 60/4 = 15.
Calculate: 2¼ × 2/3
Answer: 3/2 or 1½
2¼ = 9/4. Then (9×2)/(4×3) = 18/12, which simplifies to 3/2.
A recipe needs 3/4 cup of flour. How much for 2/3 of a batch?
Answer: 1/2 cup
3/4 × 2/3 = 6/12 = 1/2 cup.
Calculate: 1/2 × 2/3 × 3/4
Answer: 1/4
Multiply across: 6/24, which simplifies to 1/4. Cancelling first is faster.
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Every student arrives with the belief that multiplication increases and division decreases, and fractions break both halves of it. Multiplying by 1/2 halves a number. This is not a special rule to memorise; it follows from reading the multiplication sign as the word 'of'. One half of three quarters is obviously smaller than three quarters, and once students hear the sentence that way the surprise disappears.
The same reading makes word problems tractable. Two thirds of a batch, three quarters of a class, half of a remaining amount are all multiplications, and students who translate 'of' into × solve them without needing to identify a problem type.
Multiplying 4/9 × 3/8 straight across gives 12/72, which then has to be simplified by 12. Cancelling first turns the same question into 1/3 × 1/2 and the arithmetic becomes trivial. The two routes give the same answer, but the second produces far fewer errors because the numbers stay small.
The rule is that any numerator can cancel with any denominator, not just the one directly beneath it. Students who understand this handle three-fraction products comfortably; students who do not end up multiplying large numbers and then struggling to simplify them.
✗ Finding a common denominator before multiplying.
✓ Common denominators are only needed for addition and subtraction. Multiply straight across instead.
✗ Multiplying a mixed number without converting it first.
✓ Convert to an improper fraction. Multiplying the whole parts and fractions separately gives the wrong answer.
✗ Expecting the product to be larger than both fractions.
✓ Multiplying by a fraction less than 1 makes a number smaller. Half of three quarters is less than three quarters.
✗ Leaving the answer unsimplified.
✓ Divide the numerator and denominator by any common factor. Cancelling before multiplying avoids large numbers entirely.