Black Friday

Number Theory Level 2

Given that in a certain year: November had a Friday the 13th, what is the probability that February (of the following year) had a Friday the 13th as well?

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3 7 \frac 3 7 2 7 \frac 2 7 1 7 \frac 1 7 6 7 \frac 6 7 0 7 \frac 0 7 5 7 \frac 5 7 4 7 \frac 4 7 7 7 \frac 7 7

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Chung Kevin by Chung Kevin , 45, Australia

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1 solution

Utkarsh Singh
Apr 16, 2015

You can simply count it. On 13th Feb of the following year it will be a Saturday. Hence the required event is impossible.

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Right! What do you think is the simplest way to count it?

Chung Kevin - 6 years, 1 month ago

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Well, using your fingers?

Utkarsh Singh - 5 years, 10 months ago

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