Mental maths · lesson 26 of 28 · free

Fractions as decimals by heart — Mental Maths Mastery

A few fraction families turn up again and again. Learn one member of each family and the rest follow: eighths go up in 0.125, fifths in 0.2, ninths repeat one digit, elevenths repeat 9 × the top, and sevenths go round the circle 142857.

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How to do it in your head

Know the families — “quarters, fifths, eighths, ninths, elevenths and sevenths each follow a pattern”

Quarters, fifths, eighths: 1/4 = 0.25, 1/5 = 0.2, 1/8 = 0.125 — multiply by the top number.
Ninths repeat the top number (4/9 = 0.444…); elevenths repeat 9 × the top (3/11 = 0.2727…).
Sevenths use the digits 142857 in a circle: start at the first digit of 10 × top ÷ 7.

Use it for: Percentages, money, marks out of 8 or 9, and comparing fractions quickly.

🧮 Check your own sums with the free Fraction calculator — it shows the working.

Worked example: 5/8 as a decimal = 0.625

1/8 = 0.125 (half of 0.25).
5 × 0.125 = 0.625.

Check: 0.625 × 8 = 5 ✓

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✓ Written and checked by the TalentJR team · Updated 13 Oct 2026 · How we make our lessons

✏️ Practice

Work it out in your head or on paper, then tap your answer — or type it and press Check. Stuck? Press “Show me how”.

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🏁 Lesson 26 test

20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.

🏅 Sign in with Google to earn the 🔓 Fraction Decoder badge when you pass — and a certificate when you finish all 9 lessons of Part 4 · Bigger numbers, fractions and the calendar. You can still take the test without signing in.

🖨️ Fraction to Decimal Conversion Worksheet

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