Withdrawing Balls

Probability Level 1

There are 15 balls in a basket, 3 red, 5 green and 7 blue balls. The minimum number of balls that must be withdrawn to ensure that at least one ball of each color will be obtained is:

10 3 13 8

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Frederico Chaves by Frederico Chaves , 30, Brazil

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2 solutions

Considering the worse case scenario:

  1. Draw the 7 blue balls.

  2. Followed by the 5 green balls.

  3. Then we need one red ball to have one color each.

So we need to draw a minimum of 7 + 5 + 1 = 13 balls.

1 Helpful 0 Interesting 0 Brilliant 0 Confused
Frederico Chaves
Feb 15, 2018

To ensure that at least one ball of each color will be withdrawn, we need to think at the worst case, that is, withdrawing 7 blue balls, 5 green balls and finally 1 red ball. So, the minimum number of balls are 13.

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