Sargataur
unless theres a catch to this question or im not reading it right
1/4 marked with one mark = 1/4 of 4000 = 1000 fishes
400 fishes with 2 or more marks
so total marked fishes = 1400 of which reqd prob is 1000/1400 = 10/14
but i doubt the question is that easy....
what od u guys think ....71.5 percent or 0.715
target780, Sargataur,
Yes, the word 'at least 1/4' is part of the question stem [I am dead sure about this]. And No the answer is NOT 5/7 since this was "not" one of the five answer choices.
I too believe having 'at least' makes the problem unbounded and therefore this makes a good tricky problem which the ETS loves to throw into the questions.
Can anyone else give this problem a try.
If this were a data sufficiency question I would say it is solvable, but it seems to be impossible to solve by hand. Since the probability is the number of favorable outcomes/total outcomes, you could add up the probability with 1/4 marked, then keep adding 1 more fish till you have all of them, or start with 0 marked, then go up to 1/4 and subtract 1 from this answer. Maybe there is some kind of pattern that would make any of these calculations possible but I don't know.