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ELI5 Yahaaa

Ten per cent, then adjust

How Do People Work Out a Tip in Their Head?

Nobody calculates a tip exactly — they find ten per cent and nudge it.

1 The bill is £462 10% is £4.603 Half againmakes £6.90 —call it £7
A tip is an estimate wearing a percentage costume.

  1. Step 1 of 5

    Ten per cent needs no arithmetic.

    Long division?46 ÷ 10, worked outMoving the point £46 → £4.60, instantly

    Move the decimal point one place left and you have it. £46 becomes £4.60 without a single calculation.

  2. Step 2 of 5

    Everything else is built from that.

    5%half of ten10%the one you cansee20%ten, doubled

    Five per cent is half of ten. Fifteen per cent is ten plus half of ten. Twenty per cent is ten doubled. No new sums.

  3. Step 3 of 5

    Then you round to something friendly.

    1 £6.90 exactly2 Round up3 £7 — same tip,easier maths

    Nobody hands over £6.90. Rounding to £7 changes the tip by pennies and makes the total easy to check.

  4. Step 4 of 5

    Rounding the bill first is faster still.

    Exact?10% of £46 = £4.60Rounded first+10% of £50 = £5.00

    Treat £46 as £50, take ten per cent, and you get £5. You have over-estimated by pennies and saved yourself the awkward numbers.

  5. Step 5 of 5

    Which is why estimating is the real skill.

    Exact answerslow, and nobodychecksClose estimatefast, and goodenough

    The tip does not need to be right — it needs to be close and quick. Being able to land within a few per cent is worth more than exactness.

    Some countries build service into the price precisely to remove this sum from the end of a meal.

The short version

Tips are found by moving the decimal point one place, building other percentages from that, and rounding to something friendly.

Try it yourself

Work out 12.5% of £64 in your head: 10% is £6.40, a quarter of that is £1.60, so £8.

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