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In a box there are red and blue balls. If you select a handful of them with
eyes closed, you have to grab at least
of them to make sure at least one of
them is red and you have to grab at least
of them to make sure both colors
appear among the balls selected. How many balls are there in the box?
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1 solution
If 5 balls are needed to make sure at least one of them is red, that means that there are 4 blue balls in the box. If you need 1 0 to make sure both colors appear then there are 9 balls of the more used color –which must be red. Therefore there are 9 + 4 = 1 3 balls in the box.