There are two stages: 1. A coin is chosen at random. So, ‌P(‌ blue coin ‌)=‌
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‌P(‌ red coin ‌)=‌
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2. The chosen coin is tossed. We want P( Head ). Use the law of total probability: P(‌ Head ‌)=P(‌ Head ‌∣‌ blue ‌)⋅P(‌ blue ‌)+P(‌ Head ‌∣‌ red ‌)⋅P(‌ red ‌) Substitute the values: P(‌ Head ‌)=0.99⋅‌