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Grade 8 Probabilities That Sum to One Worksheets

Use the fact that every outcome together has probability 1 to find a missing one.

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Probability · Grade 8

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SkillEach skill is a different kind of question, with its own levels.
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Grade 8 · 3 pages · A4

Probability Practice

Grade 8 • Probabilities That Sum to One • One missing of four
Name:Date:

All the probabilities add up to 1. Write the missing one as a fraction in its simplest form.

  1. 1) A spinner can stop on green, yellow, red or brown. The probabilities of green, yellow and red are 1/4, 3/8 and 1/4. What is the probability of brown?
    Answer:
  1. 2) A spinner can stop on green, white, black or yellow. The probabilities of green, white and black are 1/6, 5/12 and 1/4. What is the probability of yellow?
    Answer:
  1. 3) A spinner can stop on green, red, white or purple. The probabilities of green, red and white are 1/5, 2/15 and 3/5. What is the probability of purple?
    Answer:
  1. 4) A spinner can stop on black, green, red or brown. The probabilities of black, green and red are 3/4, 1/12 and 1/12. What is the probability of brown?
    Answer:
  1. 5) A spinner can stop on white, brown, red or purple. The probabilities of white, brown and red are 1/2, 1/10 and 1/5. What is the probability of purple?
    Answer:
  1. 6) A spinner can stop on green, pink, yellow or red. The probabilities of green, pink and yellow are 1/10, 2/5 and 2/5. What is the probability of red?
    Answer:
  1. 7) A spinner can stop on yellow, red, green or white. The probabilities of yellow, red and green are 1/2, 1/8 and 1/8. What is the probability of white?
    Answer:
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Page 1 of 3

All the probabilities add up to 1. Write the missing one as a fraction in its simplest form. (continued)

  1. 8) A spinner can stop on brown, purple, green or yellow. The probabilities of brown, purple and green are 1/6, 1/2 and 1/6. What is the probability of yellow?
    Answer:
  1. 9) A spinner can stop on green, red, yellow or orange. The probabilities of green, red and yellow are 11/20, 3/10 and 1/20. What is the probability of orange?
    Answer:
  1. 10) A spinner can stop on green, yellow, pink or black. The probabilities of green, yellow and pink are 7/10, 1/10 and 1/10. What is the probability of black?
    Answer:
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Page 2 of 3

Answer Key

  1. 1. 1/8
  2. 2. 1/6
  3. 3. 1/15
  4. 4. 1/12
  1. 5. 1/5
  2. 6. 1/10
  3. 7. 1/4
  4. 8. 1/6
  1. 9. 1/10
  2. 10. 1/10
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Page 3 of 3

What each level generates

Grade 8 probabilities that sum to one — the exact skill behind each difficulty setting, straight from the generator.

  1. Level 1One missing of three
  2. Level 2One missing of four
  3. Level 3The rest, shared equally

Grade levels follow the progression common to most English-language curricula — not one specific national curriculum. Every level shows exactly what it generates, so you can check the fit with your own program. See the full scope & sequence →

More Grade 8 probability skills

Each one generates a different kind of question, with its own three levels and answer key.

Frequently asked questions

▸Does Common Core cover probability at Grade 8?

Not as probability. The Grade 8 Statistics and Probability standards cover scatter plots, lines of best fit and two-way tables. These sheets carry the Grade 7 probability work forward, in step with the Australian Year 8 and Ontario Grade 8 chance strands and England's Key Stage 3.

▸How do you find a missing probability?

Subtract the ones you have from one, since every possible outcome together must total one. On the third level the remainder is then shared equally between two outcomes, so there is a halving after the subtraction.

▸What does 'without replacement' change?

Both parts of the second fraction. Taking a red counter from three red and five blue leaves two red out of seven, so the second probability is 2/7 and not 3/8. Multiplying gives 3/28.

▸Are there tree diagrams to fill in?

No — every question is set out in a sentence and answered with a single probability. A tree is a good way to organise the work and your child can draw one on scrap paper, but nothing on the sheet requires it.

▸Is this worksheet generator free?

Yes — free, no sign-up, and no watermark. The link in the address bar reprints the identical sheet whenever you want it.