KöMaL 2009 C992
To boost the sales of a certain kind of sweets, the manufacturing company encloses gift vouchers in some of the boxes. The managers consider that the campaign will be efficient and costs will be bearable if the probability for a customer buying 10 boxes of sweets to find at least 1 voucher is about 50%. One in how many boxes should contain a voucher to achieve that?
Official text KöMaL. Quoted with source.
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