Example 1: Two proper fractions
Calculate 3/4 ÷ 1/2.
- 1Keep 3/4 as it is.
- 2Change ÷ to ×.
- 3Flip 1/2 to 2/1.
- 4Multiply: (3 × 2) / (4 × 1) = 6/4 = 3/2.
Answer: 3/2 or 1½
To divide by a fraction, multiply by its reciprocal. The method takes one line, but it is worth understanding why it works, because dividing by a fraction usually makes the answer bigger and that surprises students every year.
a/b ÷ c/d = a/b × d/c
Keep the first fraction, change the division to multiplication, and flip the second fraction. The flipped fraction is called the reciprocal. Once the question is a multiplication, the usual rules apply: multiply across and simplify.
Calculate 3/4 ÷ 1/2.
Answer: 3/2 or 1½
Calculate 2/3 ÷ 4.
Answer: 1/6
How many quarter-cups are in 2 cups?
Answer: 8 quarter-cups
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 ÷ 1/4
Answer: 2
Flip and multiply: 1/2 × 4/1 = 4/2 = 2.
Calculate: 3/5 ÷ 1/5
Answer: 3
3/5 × 5/1 = 15/5 = 3.
Calculate: 1/3 ÷ 2
Answer: 1/6
1/3 × 1/2 = 1/6.
Calculate: 4/5 ÷ 2/5
Answer: 2
4/5 × 5/2 = 20/10 = 2.
Calculate: 2/3 ÷ 3/4
Answer: 8/9
2/3 × 4/3 = 8/9.
Calculate: 5/8 ÷ 5/6
Answer: 3/4
5/8 × 6/5 = 30/40 = 3/4. Cancelling the 5s first is faster.
How many 1/3 cups are in 2 cups?
Answer: 6
2 ÷ 1/3 = 2 × 3 = 6 one-third cups.
Calculate: 1½ ÷ 3/4
Answer: 2
1½ = 3/2. Then 3/2 × 4/3 = 12/6 = 2.
A 3/4 metre ribbon is cut into 1/8 metre pieces. How many pieces?
Answer: 6 pieces
3/4 ÷ 1/8 = 3/4 × 8/1 = 24/4 = 6.
Calculate: 2¼ ÷ 1½
Answer: 3/2 or 1½
9/4 ÷ 3/2 = 9/4 × 2/3 = 18/12 = 3/2.
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Dividing by 1/2 asks how many halves fit into the amount, and there are twice as many halves as wholes, so the answer doubles. Dividing by 1/4 quadruples it. Read that way, multiplying by the reciprocal is not a trick but a restatement of the question, and students who see this stop flipping the wrong fraction because they can sanity-check the size of their answer.
The measuring-cup framing is the fastest route to this understanding. Ask how many quarter-cups are in two cups before showing any algorithm, and the answer of eight is obvious. The formal method then arrives as a shortcut for something already understood rather than as a rule to trust blindly.
Because dividing by a fraction less than 1 increases the value, students can predict roughly what the answer should be before doing any arithmetic. In 2/3 ÷ 3/4 the divisor is close to 1, so the answer should be close to 2/3, and 8/9 is plausible. In 3/4 ÷ 1/8 the divisor is tiny, so the answer should be several times larger, and 6 is plausible.
This estimate catches the flip-the-wrong-fraction error immediately, since that mistake usually produces an answer of obviously the wrong size. Building the habit costs one extra sentence per question and removes most of the marks lost in this topic.
✗ Flipping the first fraction instead of the second.
✓ Only the divisor, the fraction after the division sign, is flipped. The first one is kept unchanged.
✗ Flipping the second fraction but leaving the division sign.
✓ The operation must change to multiplication at the same moment the fraction is flipped.
✗ Assuming division always makes the answer smaller.
✓ Dividing by a fraction less than 1 gives a larger answer, because you are counting how many small pieces fit inside.
✗ Dividing mixed numbers without converting them.
✓ Convert both to improper fractions before flipping. 1½ must become 3/2 first.