31 Coin Tosses

Probability Level 4

31 coins are tossed.

The probability that heads comes on $n$ of them, where $1 \equiv n \mod 3$ , is

\dfrac{1}{2}

\dfrac{1}{4}

None of these

\dfrac{1}{3}

1 solution

Pratik Shastri
Sep 9, 2014

Incidentally the difference between the correct answer and $\dfrac{1}{3}$ approximately $1.55 \times 10^{-10}$

The exact answer is $\frac{1}{3}(1-\frac{1}{{2}^{31}})$

Ronak Agarwal - 6 years, 8 months ago

I think there should be a positive sign

Pratik Shastri - 6 years, 8 months ago

So, I marked $\frac{1}{3}$ , as the correct answer, since it doesn't ask for the exact answer. Actually, I found $\frac{1}{3}\left(1+\frac{1}{2^{31}}\right)$ . I don't think you made a wise choice by making it as multiple choice question.

Dieuler Oliveira - 6 years, 7 months ago

Well, not asking for an approximate answer is equivalent to asking for an exact answer, isn't it?

Pratik Shastri - 6 years, 7 months ago

the same mistake as I did.

mudit bansal - 6 years, 4 months ago

31 Coin Tosses

1 solution

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