Official Solution:

There are 15 black chips and 5 white chips in a jar. What is the least number of chips we should pick to guarantee that we have 2 chips of the same color?

A. 19
B. 16
C. 6
D. 5
E. 3

Worst case scenario would be if the first two chips we pick will be of the different colors. But the next chip must match with either of two, so 3 is the answer.

Answer: E
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That's a simple one. If we take three , at least two will be of same type. Hence, answer is 3.

I don't understand what you mean there...

Check other Worst Case Scenario Questions from our Special Questions Directory to understand the concept better.
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What is the least number of chips we should pick to guarantee that we have 2 chips of the same color? So, we need to have tow white or two black chips.

The worst case would be if for the first two pick we'll get one black and one white chips: BW or WB. The next (3rd) chip will be B or W in any case we'll have two chips of the same color: BW - W or BW - B.

You should check other worst case scenario questions. Link is in the post above.
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Hi Bunuel

Please help me understand this.

IMO,

For a best scenario(Least no of picks) We should select minimum 6 to ensure that one color chips are exhausted.
For a worst scenario(Max no of picks) we should select minimum 17 to ensure the same.

If we are picking 2, then why are we considering the third to be of the other color ? why not of the same color as we have picked before ?

Please help me evaluate my thought process.

Hi

Can someone explain how this question is different from the one below:

A box contains 10 tablets of medicine A and 15 tablets of medicine B. What is the least number of tablets that should be taken from the box to ensure that at least two tablets of each kind are among the extracted?
(source: GMAT Club forums)

In this question, we want to ensure, to guarantee that we have 2 chips of the same color? So, we need to have tow white or two black chips. The worst case would be if for the first two pick we'll get one black and one white chips: BW or WB. The next (3rd) chip will be B or W in any case we'll have two chips of the same color: BW - W or BW - B.



In this question, we want to ensure, to guarantee that we have at least two tablets of each kind are among the extracted. So, we need AABB. The worst case would be if we pick all 15 tablets of medicine B first: BBBBBBBBBBBBBBB. We will be left with 10 tablets of of medicine A. So, the next 2 tablets we remove have to be of medicine A, so we'd have BBBBBBBBBBBBBBBAA. This gives us at least two tablets of each kind.

Check other Worst Case Scenario Questions from our Special Questions Directory to understand the concept better.

Hope it helps.
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Please read the question carefully!

There are 15 black chips and 5 white chips in a jar. What is the least number of chips we should pick to guarantee that we have 2 chips of the same color?

A. 19
B. 16
C. 6
D. 5
E. 3
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