How to Divide by 5 in Your Head
Level 1 Mental division · Reviewed by The NumThink editorial team · Last reviewed
Short version: To divide by 5, double the number and divide by 10: 340 ÷ 5 → 680 ÷ 10 = 68.
This page is part of the NumThink Mental division course. Read why the method works, watch it run on worked examples, then drill it in the practice box below until it feels automatic.
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Dividing by 5 is the same as dividing by 10 and multiplying by 2. Doing the easy half first — doubling — turns the problem into "drop a zero": n ÷ 5 = (n × 2) ÷ 10.
It mirrors the ×5 trick exactly (×10 then halve), so the two methods reinforce each other.
The steps
- Double the number. 340 × 2 = 680.
- Drop the zero. 680 ÷ 10 = 68. Done.
Worked examples
Easy 45 ÷ 5
Show the thinking
45 × 2 = 90
90 ÷ 10 = 9.
Answer: 9
Medium 340 ÷ 5
Show the thinking
340 × 2 = 680
680 ÷ 10 = 68.
Answer: 68
Hard 2,150 ÷ 5
Show the thinking
2,150 × 2 = 4,300
4,300 ÷ 10 = 430.
Answer: 430
When to use it
- Any division by 5 — and by extension by 50 (double, drop TWO zeros) and 500.
- Odd numbers too: 87 ÷ 5 → 174 ÷ 10 = 17.4 — the method handles decimals gracefully.
When NOT to use it
- When you already see the answer (25 ÷ 5 = 5 from memory).
- Divisions by 25 — use the ÷25 method instead of doubling twice manually.
Common mistakes
Dividing by 10 first. 340 ÷ 10 = 34, then doubling to 68 — works, but any number not ending in 0 turns into a decimal mid-way (87 ÷ 10 = 8.7). Fix: Double FIRST, then the ÷10 step is free.
Dropping the wrong number of zeros. Dropping two zeros for ÷5. Fix: ÷5: one zero. ÷50: two zeros. Count the zeros in the divisor.
Check yourself: Reverse it: 68 × 5 must equal 340 — and multiplying back by 5 is a method you already own.