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 5 of them to make sure at least one of them is red and you have to grab at least 10 of them to make sure both colors appear among the balls selected. How many balls are there in the box?
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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 5 of them to make sure at least one of them is red and you have to grab at least 10 of them to make sure both colors appear among the balls selected. How many balls are there in the box?
"you have to grab at least 5 of them to make sure at least one of them is red"
This tells me that there are four blue balls.
"you have to grab at least 10 of them to make sure both colors appear among the balls selected"
This tells me that there are nine red balls.
4 blue + 9 red = 13 balls total
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