If a fair coin is tossed twice, find the probability of getting 'atmost one head'.
Generated by claude-sonnet-4-6 · 2026-06-15 10:30 · grounding rag
Model Answer
When a coin is tossed twice, the sample space is: {HH, HT, TH, TT} → Total outcomes = 4
Event: 'at most one head' means 0 or 1 head.
Favourable outcomes: {TT, HT, TH} → 3 outcomes
$$P(\text{at most one head}) = \frac{3}{4}$$
Source: Chapter 14 – Probability, Section 14.1
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Explanation
- "At most one head" means 0 heads or 1 head — do not include HH.
- Always list the sample space first; examiners award a mark for it.
- The 2 marks are typically split: 1 for correct sample space/favourable outcomes, 1 for the final probability.
- A common error is writing only 3 outcomes in the sample space (treating HT and TH as the same) — they are distinct outcomes.