Evaluating expected outcomes
I'm analyzing expected costs based on how soon 3 heads show up in 5 tosses: 240, 320, 400, or 480. Now I need to calculate E[X].
Clarifying event probabilities
I'm piecing together that events A_3, A_4, and A_5 denote getting 3 heads for the first time on the 3rd, 4th, and 5th tosses.
Examining the ambiguity
The phrase "前3次連續擲得3個正面者" could mean "the first 3 tosses are heads in a row." This makes me think the probability for event E1 is 1/8.
Assessing coin toss odds
I'm working through calculating the probability of getting exactly 2 heads in the first 3 tosses, followed by a head on the 4th toss, which equals 3/16.
Calculating probabilities
I'm piecing together the probability of getting exactly 2 heads in the first 4 tosses and then a head on the 5th toss, which is 3/16. Noticing the exclusion of earlier heads.
Ensuring accurate probabilities
I determined that the probability for event E2 is 3/16, confirming 3 heads in the first 3 tosses and a head on the 4th.
Assessing probabilities
I found the probability for event E3 is 3/16: precisely 2 heads in the first 4 tosses, then a head on the 5th, without earlier accumulations.
Breaking down probabilities
I determined that the probability of not achieving 3 heads in 5 tosses is 1/2. This entails considering 0 to 2 heads in 5 tosses.
Summing probabilities
I verified that the probability of achieving 3 heads in 5 tosses is 1/2, combining the outcomes of exactly 3, 4, or 5 heads.
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