[GMAT math practice question]
A box contains 3 red balls, 4 green balls, 5 yellow balls, 6 blue balls and 7 white balls. What is the minimum number of balls that must be drawn from the box without replacement to guarantee that at least 5 balls of a single color will be drawn?
A. 10
B. 12
C. 15
D. 18
E. 21
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A box contains 3 red balls, 4 green balls, 5 yellow balls, 6
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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 5 of the same color:Max@Math Revolution wrote:[GMAT math practice question]
A box contains 3 red balls, 4 green balls, 5 yellow balls, 6 blue balls and 7 white balls. What is the minimum number of balls that must be drawn from the box without replacement to guarantee that at least 5 balls of a single color will be drawn?
A. 10
B. 12
C. 15
D. 18
E. 21
3 red
4 green
4 yellow
4 blue
4 white
Sum = 3+4+4+4+4 = 19
Implication:
It is possible to remove 19 balls without selecting 5 of the same color.
Thus, to GUARANTEE that 5 of the same color are removed, we must remove ONE MORE ball:
19+1 = 20
The correct answer is not among the answer choices.
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I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
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Scott@TargetTestPrep
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We could have 3 red balls, 4 green balls, 4 yellow balls, 4 blue balls, and 4 white balls drawn, that is, a total of 19 balls drawn, without 5 balls of a single color drawn. However, the next ball drawn will be yellow, blue or white, and we will have 5 balls of a single color drawn. Therefore, we need to draw 20 balls to guarantee that at least 5 balls of a single color will be drawn.Max@Math Revolution wrote:[GMAT math practice question]
A box contains 3 red balls, 4 green balls, 5 yellow balls, 6 blue balls and 7 white balls. What is the minimum number of balls that must be drawn from the box without replacement to guarantee that at least 5 balls of a single color will be drawn?
A. 10
B. 12
C. 15
D. 18
E. 21
Answer: 20
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Max@Math Revolution
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=>
The maximum number of draws we can make without drawing 5 balls of a single color is 3 + 4 + 4 + 4 + 4 = 14. This occurs when we draw 3 red balls, 4 green balls, 4 yellow balls, 4 blue balls and 4 white balls. If we draw one more ball, then we will have drawn 5 balls of a single color.
Thus, to guarantee that we have drawn at least 5 balls of a single color, we must draw 14+1 = 15 balls.
Therefore, C is the answer.
Answer: C
The maximum number of draws we can make without drawing 5 balls of a single color is 3 + 4 + 4 + 4 + 4 = 14. This occurs when we draw 3 red balls, 4 green balls, 4 yellow balls, 4 blue balls and 4 white balls. If we draw one more ball, then we will have drawn 5 balls of a single color.
Thus, to guarantee that we have drawn at least 5 balls of a single color, we must draw 14+1 = 15 balls.
Therefore, C is the answer.
Answer: C
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regor60
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Max@Math Revolution wrote:=>
The maximum number of draws we can make without drawing 5 balls of a single color is 3 + 4 + 4 + 4 + 4 = 14. This occurs when we draw 3 red balls, 4 green balls, 4 yellow balls, 4 blue balls and 4 white balls. If we draw one more ball, then we will have drawn 5 balls of a single color.
Thus, to guarantee that we have drawn at least 5 balls of a single color, we must draw 14+1 = 15 balls.
Therefore, C is the answer.
Answer: C
The highlighted calculation adds up to 19 not 14
