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probability

by vipulgoyal » Wed Mar 06, 2013 2:36 am
if a number is drawn from the first 1000 positive integers, what is the probility of selecting a refined number.

1) any refind number must be divisible by 22
2) A refined number is any even multiple of 11

at the first sight ans seems D but it is B, experts please shed some light
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by Zarrolou » Wed Mar 06, 2013 3:08 am
vipulgoyal wrote:if a number is drawn from the first 1000 positive integers, what is the probility of selecting a refined number.

1) any refind number must be divisible by 22
2) A refined number is any even multiple of 11
Meybe the trick is this: "any refind number must be divisible by 22" but this doesn't define what a refind number is.
For example: must be divisible by 22, AND BY 3.

Option B, on the other, hand defines what a refined number is...

My opinion
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by Anurag@Gurome » Wed Mar 06, 2013 3:13 am
vipulgoyal wrote:if a number is drawn from the first 1000 positive integers, what is the probility of selecting a refined number.

1) any refind number must be divisible by 22
2) A refined number is any even multiple of 11
I guess this is a DS problem posted in wrong forum.

Anyway, the required probability = (Number of refined numbers in first 1000 positive integers)/1000
Hence, we need to know what is refined number and how many of them are in the first 1000 positive integers.

Statement 1: This is not a complete definition of refined number. There may be some other criteria like divisible by 3 or perfect square or sum of digits equal to 9 to be a refined number. Hence, we cannot find out the number of refined number in the first 1000 positive integers.

Not sufficient

Statement 2: Now we know that any even multiple of 11 is a refined number. Hence, we can find out the number of even multiples of 11 in the first 1000 positive integers.

Sufficient

The correct answer is D.
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