Gregsterh wrote:

Question: if we know, that the probability of picking a boy (=student) who is better that 50%, do we really have to know any more information about the rest to answer the question?

In my understanding, the rest consists of a. boys below 50%, b. girls above 50%, c. girls below 50% (consolidated = other 50% of total of students).

Therefor I know, that whatever comes in addition, we for sure have a probability of greater 50% (if we have at least 1 girl who is better than 50%), and the given information in 1) is sufficient to answer. Because at least half of the total students are boys better than 50%.

If this is not the case the question is probably missleading the way it's stated.

Let me know what you think.

Hi..

Question is perfectly fine and means exactly what it is intended to..

You are taking students as only boys which is wrong.. students will consist of both boys and girls.

The main statement tells us - Do 1/4 or 25% of students have got more than 50% marks..

1) statement I tells us that 50% of boys have got more than 50% marks..

If boys are 2 and girls 40.. boys Both >50% and 2 girls >50%.. overall 4 out of 42 students>50% , so ans is NO

If there are 40 boys and 10 girls, Ans is always YES

Insufficient

Hope it helps

I hope I will not see such a question on the real exam, as I understood the statement #1 exactly as Gregsterh did: the probability of choosing a student who is a boy AND also got more than 50% is 1/2. In that case statement#1 alone is sufficient indeed.