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Tossing coins: one, two and three sheet
3-mark answer frame

Three coins are tossed together. Find the probability of getting (i) exactly one head, (ii) at least one head, (iii) at most two heads.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Write what is given and what is to be found. Three coins are tossed. To find: P(exactly one head), P(at least one head), P(at most two heads).
  2. 2 · List all the outcomes. HHH, HHT, HTH, THH, HTT, THT, TTH, TTT. Total = 8.
  3. 3 · Write the formula. P(E) = favourable outcomes ÷ total outcomes.
  4. 4 · Count for each event.
    • Exactly one head: HTT, THT, TTH (3). P = 3/8.
    • At least one head: all except TTT (7). P = 7/8.
    • At most two heads: all except HHH (7). P = 7/8.
  5. 5 · Check and box the answer. Check (ii) with the complement: 1 − P(no head) = 1 − 1/8 = 7/8. Box all three answers.

Scoring tip: Write all 8 outcomes in a neat list first. Most errors come from a missing outcome.