In a jar there are 21 white balls, 24 green balls and 32 blue balls. How many balls must be taken out in order to make sure we have 23 balls of the same color?

a) 23
b) 46
c) 57
d) 66
e) 67
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Here, we need to find minimum number of marbles to be taken out to get 23 marbles of same color.

For a instance, if we take 21 white marbles 1st and followed by 22 Green and then 22 Blue.

Total will be 21 + 22+ 22= 65 draws.

If we choose either Green or Blue next time. This will bring the total of either of these colored marble to 23.

So Minimum we need to take 65+1 = 66 Times to get 23 marbles of same color(either Green or Blue).

Answer : D.

Hope it helps.
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The answer is 23.

Remember? The balls are in a jar. Jars are made of glass so you can see the colors of the ones that you wanted to take out.

Actually, the wording of the question is quite standard. How many do you need to take out to ensure that you have 23 of the same colour? means that out of the balls taken out, we need to ensure that there should be 23 of the same colour.
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Think about a simpler case.
Say you have a box with 2 red balls, 2 blue balls and 2 white balls. Now you need to take out some balls to ensure you have two fo the same colour. How many balls do you need to take out to ENSURE that you have 2 balls of same colour.
Say, you took out a red ball. Then a blue ball. Then a white ball. You still don't have 2 balls of same colour. Now the next ball you take out will make it two balls of same colour. So we need to take out 4 balls to ENSURE that there are 2 of the same colour.

This is the same case here. Now, review the original question and solution.
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We are taking only 22 marbles for Green because 1 more marble would suffice our need i.e. 23 marbles of same colour. So we are trying to reach a case where we are just one short of a marble such that any marble pick would help in reaching the required condition.