kuvshah wrote:

What I am reading wrong here? 11 ticks are for 30 years or older and 5 ticks for 30 years and older and no diploma. that's total 35 ticks for 30 years and older and 9 tickets for no dipolma. there are 10 ticks outside the both circles. those 10 ticks are 30 years and under and with high school diploma - so Number of students who are under 30 or high school graduates is 100/300 = 1/3 but OA is 5/6.

Where did i commit mistake in understanding the diagram?

Dear

kuvshah,

I'm happy to respond.

My friend, I think you are getting confused on "

and" and "

or." Those are absolutely crucial words in probability. You were basically correct for counting ticks in groups. There are 30 ticks total.

Group A = 30 or older AND has HS diploma (left lune) = 11 ticks

Group B = 30 or older AND has no HS diploma (overlap) = 5 ticks

Group C = under 30 AND has no HS diploma (right lune) = 9 ticks

Group D = under 30 AND has HS diploma (outside both circles) = 10 tickets

Question #1:

If one student is selected at random from the 300 surveyed, the chance that the student will be under 30 AND a high school graduate is ________ .

That's Group D only, over the whole, 10/30 = 1/3. That's the correct answer, but this was NOT the question asked in this problem.

Question #2:

If one student is selected at random from the 300 surveyed, the chance that the student will be under 30 OR a high school graduate OR both is ________. This is the actual question asked in this IR problem, and the answer group is A & B & D, those three groups over the whole.

Group A people have the HS diploma, so they are in.

Group B people are under 30, to they are in.

Group D people are in on both counts.

All of these people are in (the only people not in are the 5 ticks in the overlap). Thus, 25 ticks over 30 ticks, 25/30 = 5/6.

You found the correct answer to the wrong question. Does this make sense?

Mike

_________________

Mike McGarry

Magoosh Test Prep