# Mathematical Food for Thought

Serves a Daily Special and an All-You-Can-Eat Course in Problem Solving. Courtesy of me, Jeffrey Wang.

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Something To Think About. Topic: Probability. Level: AMC/AIME. April 18th, 2007

Problem: A coin is repeatedly flipped. What is the expected number of flips to get two heads in a row? heads in a row?

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I will be out of town for the next four days, so have fun with the problem!

### 4 Responses to “Something To Think About. Topic: Probability. Level: AMC/AIME.”

1. Xuan Says:

four times for the two heads in a row
and… 2n for n heads in a row

wahhhhhhh

so ur at stanford?? u miss out on concessions… MOOO

Yeah, I’m at Stanford right now. And both of your answers are wrong =P.

3. t0rajir0u Says:

Xuan, those answers are correct for n heads total, but it takes a lot more effort to get them all in a row.

Anyway, the recursion for n looks really ugly…

4. 4PV-177945 - Besa Pendant Says:

Another Day, Another Post

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