Probability to get a lucky draw?

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Yesterday we had annual dinner with all colleague. Of course, lucky draw must be carried out.

All of our names were written in a piece of small paper for each and thrown into a box. The lucky draw was performed about 30 rounds. Each time a paper was pulled out, the person with the name same as the one from that paper would get a gift. After that that paper was discarded (without replacement).

Everyone was excited. All hoped to get drawn out. Suddenly I was thinking, what is the chance for me to get a gift?

Yeah, I don’t need a precise number but just a rough one. So I took this formula from Excel:

BINOM.DIST.RANGE(30,1/500,1) = 5.66%

Ah ja, of course not so accurate – no consideration of “no replacement”, and some minor one. But sure enough, it should be between BINOM.DIST.RANGE(30,1/450,1) and BINOM.DIST.RANGE(30,1/500,1). That’s 5.66% – 6.25%. Not too bad:)

And, I got one. Bingo! Lucky enough!


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