CLASS 9 MATHS · NUMBER SYSTEMS

Convert recurring decimals to p/q form

Let x be the decimal, multiply by 10, 100 … to line up the repeating part, subtract, and solve for x.

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Worked examples

Example 1 · level 1

Write 0.44444… (the 4 repeats) in the form p/q (lowest terms).

Show solution
  1. Let x = 0.4444…
  2. 10x = 4.4444…
  3. 10x − x = 4 → 9x = 4 → x = 4/9.

Answer: 4/9

Example 2 · level 2

Write 0.31313131… (the block 31 repeats) in the form p/q (lowest terms).

Show solution
  1. Let x = 0.313131…
  2. 100x = 31.313131…
  3. 100x − x = 31 → 99x = 31 → x = 31/99.

Answer: 31/99

Example 3 · level 3

Write 0.277777… (only the 7 repeats) in the form p/q (lowest terms).

Show solution
  1. Let x = 0.27777…
  2. 10x = 2.7777… and 100x = 27.777…
  3. 100x − 10x = 27 − 2 = 25 → 90x = 25 → x = 5/18.

Answer: 5/18

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