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In a certain year, the month of January had exactly $4$ Mondays and $4$ Fridays. What was the day on Gandhi Jayanti $(2^{\text{nd}}$ October $)$ the previous year?

I am not sure how to approach this one, any ideas?

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I didn't know that there is tag called calendar-computations. Thanks @J.M. :) – Quixotic Jul 21 '12 at 4:05
up vote 11 down vote accepted

As January has 31 days, there are three days that there were 5 of (pigeonhole principle). The calendar says they must be contiguous, so they must have been Tuesday, Wednesday, and Thursday. So Jan 1 was Tuesday. Then just count back.

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