[GMAT math practice question]
A box contains 1 red ball, 3 green balls, 5 yellow balls, 7 blue balls, 9 white balls, and 11 black balls. What is the minimum number of balls that must be drawn from the box without replacement to guarantee that at least 7 balls of the same color are drawn?
A. 7
B. 14
C. 15
D. 27
E. 28
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A box contains 1 red ball, 3 green balls, 5 yellow balls, 7
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Max@Math Revolution
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Determine the WORST-CASE-SCENARIO -- for each color of ball, the MAXIMUM number that can be removed WITHOUT removing 7 of the same color:Max@Math Revolution wrote:[GMAT math practice question]
A box contains 1 red ball, 3 green balls, 5 yellow balls, 7 blue balls, 9 white balls, and 11 black balls. What is the minimum number of balls that must be drawn from the box without replacement to guarantee that at least 7 balls of the same color are drawn?
A. 7
B. 14
C. 15
D. 27
E. 28
1 red
3 green
5 yellow
6 blue
6 white
6 black
Sum = 1+3+5+6+6+6 = 27.
Implication:
It is possible to remove 27 balls without selecting 7 of the same color.
Thus, to GUARANTEE that 7 of the same color are removed, we must remove ONE MORE ball:
27+1 = 28.
The correct answer is E.
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Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
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Max@Math Revolution
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The maximum number of draws without 7 balls of a single color is 1 + 3 + 5 + 6 + 6 + 6 = 27, obtained by drawing 1 red ball, 3 green balls, 5 yellow balls, 6 blue balls, 6 white balls and 6 black balls. If we draw one more ball, then we must have 7 balls of one color.
Thus, we need to draw 28 balls to ensure that 7 balls of the same color are drawn.
Therefore, E is the answer.
Answer: E
The maximum number of draws without 7 balls of a single color is 1 + 3 + 5 + 6 + 6 + 6 = 27, obtained by drawing 1 red ball, 3 green balls, 5 yellow balls, 6 blue balls, 6 white balls and 6 black balls. If we draw one more ball, then we must have 7 balls of one color.
Thus, we need to draw 28 balls to ensure that 7 balls of the same color are drawn.
Therefore, E is the answer.
Answer: E
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Scott@TargetTestPrep
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We can pull 1 red, 3 green, 5 yellow, 6 white, 6 blue, and 6 black balls, for a total of 27 balls. If we pull one more ball, we will be assured that there are at least 7 balls of the same color selected (since it has to be a blue or white or black ball).Max@Math Revolution wrote:[GMAT math practice question]
A box contains 1 red ball, 3 green balls, 5 yellow balls, 7 blue balls, 9 white balls, and 11 black balls. What is the minimum number of balls that must be drawn from the box without replacement to guarantee that at least 7 balls of the same color are drawn?
A. 7
B. 14
C. 15
D. 27
E. 28
Answer: E
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