Practical Brain teasers for parents (& kids)
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SAHM_TAN:
...I didn't choose C becos going with A and B will have different outcomes so cannot say doesn't matter
Why does A and B have different outcomes, ie. probabilities? -
arowana:
Alamak! The the Principal already removed one that does NOT contain his son's name, mean the other one in the box contains his son's name lo. It will be not wise to open the remaining ballot in the box one.
Not necessarily. The one in the box may contain another kid's name, and not his son's. This could happen if the parent is currently holding the ballot containing his son's name. -
Pen88n:
The Principal does nothing but just to remove a ballot from the 2 remaining ballots in the box. Assume he has x-ray vision and he knows exactly which ballot to remove. So after the Principal has done his job, one of the ballots that does not contain the parent's son's name will be removed from the problem.When the principal takes out one remaining ballot, he can either:
1) Put it back because it is the son's name
2) Remove it because it is not the son's name
If action is (1), definitely it is better that parent choose (A) open his original ballot. If action is (2), it points to (C) makes no difference whether choose A or B as the parent would not know for certain the ballot at hand or in the box contains his son's name. So, all options evaluated, the parent should choose (A). -
B
Always choose the other option. (switch with the host)
Edit:
If picking his child’s name is the desirable outcome, switch.
If picking his child’s name is NOT the desirable outcome, don’t switch.
The chance of picking his child’s name is higher if he switch. -
wonderm:
Why is the chance of chosing B 1/2?I will choose A because 1/3 the chance it is my child's name, if I chose B, the chance is 1/2.
Correct or not?
Not sure if I hope to get the answer right, that means no common sense leh :nailbite: -
Option
1. Principal remove a paper that is not his son’s name.
2. So left with 2 paper - one with his son name and one with another child’s name.
3. The fact is no matter how he choose between these 2 papers…his son won’t get in. If his paper is his sons name…his son won’t get in…if the paper is the other child’s name, the other child will get it…his son won’t get it…
So it doesn’t matter what he choose… -
Answer is C.
Because it's the 3 parents that want to get into the school? And, not their children?
(I know my answer sound weird. :rotflmao: ) -
if he stick to his original choice, the chance of picking his child’s name is 1/3.
If he switch, the chance of picking his child’s name is 2/3. -
Iluvmygals:
That is not how the ballot works. If he opens the ballot containing another parent's child, his own son gets in.Option
1. Principal remove a paper that is not his son's name.
2. So left with 2 paper - one with his son name and one with another child's name.
3. The fact is no matter how he choose between these 2 papers...his son won't get in. If his paper is his sons name...his son won't get in...if the paper is the other child's name, the other child will get it..his son won't get it...
So it doesn't matter what he choose..... -
limlim:
LOL... limlim is the genius that has no common sense but has a high IQ. Congratulations!if he stick to his original choice, the chance of picking his child's name is 1/3.
If he switch, the chance of picking his child's name is 2/3.
:congrats:
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