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either tennis balls or rubber balls

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sanju09 GMAT Instructor
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either tennis balls or rubber balls Post Mon Mar 05, 2012 5:40 am
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    I have a box containing 48 balls which are either tennis balls or rubber balls. What is the minimum number of balls I need to draw from the box in order to ensure that a tennis ball is drawn?

    1. The ratio of tennis balls to rubber balls is 3:1.
    2. There are 12 rubber balls in the box.

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    Brent@GMATPrepNow GMAT Instructor
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    Post Mon Mar 05, 2012 7:44 am
    sanju09 wrote:
    I have a box containing 48 balls which are either tennis balls or rubber balls. What is the minimum number of balls I need to draw from the box in order to ensure that a tennis ball is drawn?

    1. The ratio of tennis balls to rubber balls is 3:1.
    2. There are 12 rubber balls in the box.
    Notice that both statements essentially provide us with the same information: there are 36 tennis balls and 12 rubber balls.

    Whenever the two statements provide the same information, we know that the correct answer is either D or E.

    If there are 36 tennis balls and 12 rubber balls, what is the minimum number of balls we need to draw from the box in order to ensure that a tennis ball is drawn?

    Well, if we draw 12 balls, it's possible that all 12 balls are rubber balls. So, drawing 12 would not ensure that a tennis ball is drawn.

    However, if we draw 13 balls, we can be certain that a tennis ball is drawn.

    So, the minimum number of balls is 13.

    Since each statement alone provides enough information to answer the target question, the correct answer is D.

    Cheers,
    Brent

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