Students who studied < 10 = 75%
Students who studied <= 10 = 25 %

60% of 75% feel unprepared + 80% of 25% feel unprepared.
45% + 20% = 65 % feel unprepared

Hence 35 % feel prepared.

(If the percentages is confusing you assume that there were totally 100 students.)

It's also amusing to notice that since 65% is one of the answer choices and is unlike the others, so it is there for a reason. In this case it is a trap answer, since 65% is the percent that feels unprepared. So you could tell from the start the answer would be 35%.

Test prep companies love to do stuff like that but the GMAT would never make it as obvious, because a question like that likely wouldn't show proper "validity" or whatever the term is that means that people who are doing well in general are also doing well on this specific question.

vineeshp wrote:Students who studied < 10 = 75%
Students who studied <= 10 = 25 %

60% of 75% feel unprepared + 80% of 25% feel unprepared.
45% + 20% = 65 % feel unprepared

Hence 35 % feel prepared.

(If the percentages is confusing you assume that there were totally 100 students.)

Can u plz explain this part 80% of 25% feel unprepared.

We are given 80% of students who studied 10 hours or more each week feel prepared.

You're right, I also misread it.

Prepared should be 75% * 40% + 25% * 80% = 30% + 20% = 50%...

Good. Then I was not the only one getting 50% I'm glad...
Thanks.

Sorry, my bad. I took both as unprepared.

But hope you understood the solution.

If the answer is 50% of the students feel prepared, then there's a reason to worry.
That's not an option!
Somebody explain please.

ans is either 50% if we consider that rest 40% of the students who study less than 10 hours a week are prepared.

Else we can only consider the 25 students who study >= 10 hours a week and consider 80% 0f 25 = 20