## Reg: Probability

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Posts: 140

# Reg: Probability

Actually i am having a Query for probability asked in a Interview

Q:1

If i have tossed a coin for 3 times what is the chance of getting Head 2 Times

they told 2 times but how.Can any one explain.

Q:2

I am having 9 balls out of which i am having one ball with less weight each ball weight is 1 kg and the defect ball has 1 gm les in weight.
I am having a balance at once 2 balls can we weighed in two pans.

What is the probaility to find the defect ball

The answer is 3 But how.

Posts: 3,167

## Re: Reg: Probability

I am not sure if this is the right place for you to ask this kind of question, unless you were asking how to calculate it using SAS, which in that case, I can't provide the answer. That being said, you may get better answers(academic wise) elsewhere.

Q1.

When you say 'chance', I would reflect 'probability', which will never larger than 1 (I hope I am not too statistical anal here). Anyway, to anwer your question:

If you throw 3 times, then the total number of possible senario will be: 2(head,tail)*2*2=8

And the total number of 2-heads secario: 3*2/2=3, sorry don't know how to post the formula symbol.

Q2.

Can't believe they ask that in an interview. Anyway, the maxium time you need to weigh is 3. here is how:

Rondomly you picked 4 balls, one pair on each side of balance:

pair A vs. Pair B,

1. if they don't balance, then choose the lighter pair do another weighing, then you get your answer. This is the better scenario, which only takes 2 times.

2. if they do balance, then put them aside, choose another 2 pairs from remaining 5 balls, and weight

2.1  if they do balance, then you will know the unweighed left one is the culprit. 2 times.

2.2  if they don't balance, then it will take you another weighing to decide. This is the worst scenario, and it takes 3 times.

Regards,

Haikuo

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