This is a question best solved by
Venn Diagrams. Make sure you have studied that section in my
Probability Handout above of my book
and have done questions 14 to 18 before you attempt this question. Make sure you have definitely looked over my examples of how to prove two events are independent or not in those questions (as well as others earlier in the lesson).
This question is very similar to my question 18.
However, they do not give you enough information to fill in every part of your three-circle Venn diagram. Similar to what I do in my question 17, you will need to
put x in one of the missing parts of your three-circle diagram, then solve for x.
Don't enter percentages into your Venn, use decimals to set up for the format StatsPortal wants for your answers. For example, if the percentage is 32.15%, enter that as 0.3215 in your Venn.
You are given the percentage that follow all three sports, so you can put that value in the centre of your three-circle diagram. You are given the percentage that are
SK and
SS fans, so you can fill the appropriate region in such that the two regions representing
SK and SS add up to this given percentage. You are also given the percentage that are
SK and SB fans. Again, there are two regions in the diagram representing that, and you already know the number in one of them, so you can fill in the missing part knowing the total must be this
SK and SB amount.
Here is where things get tough. You are not given
SB
and SS, so put
x in that region that you are missing.
Now, we go to the first piece of info. We are told the percentage that are
SK fans. There are four regions in the
SK circle in your diagram, and you should have numbers already in three of them, so you can figure out what value to put in that fourth region to make the total correct.
We are also given the percentage that are
SB fans. The problem is that we have
four regions in the
SB circle but only have two numbers filled in. First add those two numbers and subtract from the total
SB percentage. For example, if you have 70% that are SB fans, and the two given regions add up to 30%, that leaves 70-30=40% to put in the remaining two regions. One of those regions is already labelled
x, so that means the remaining region can be labeled
0.40-x. Of course, these are not your numbers.
We
are also given the percentage that are
SK or SS fans. There are six regions in your diagram that represent
SK or SS. You already have numbers labeled in four of them (the four in the
SK circle). Add those four up and subtract them from the
SK or SS amount to see what is remaining. For example, if you know 40% follow SK , and 52% follow
SK or SS then we know that 52-40=12% remains to put in the two remaining regions of the
SS
circle. One of those regions we have already labeled
x so we will label the other region
0.12-x. Again, these are not your numbers, of course.
Finally, we are given the percentage that are
SB or SS followers. Add those six regions up. You will note that, besides the numbers, you will be adding
-x + x + (-x). This collects up to just
-x. Of course, there are also a bunch of
numbers you can add up in those six regions, so, if all the numbers add up to say 62%, then we discover the six regions add up to
0.62-x. But we can set that equal to the percentage that do follow
SB or SS and solve
x.
Once you have solved
x, you are rolling.
Don't even think about asking me any more questions about this one. I have told you too much as it is. You are on your own from there.
Note, in
part
(a), when they ask how many outcomes there are, count every single region in your Venn diagram to count all the possible outcomes. For example, a classic two-circle Venn diagram like my question 16, has four separate regions (four separate probabilities or percentages are labelled in the diagram). Therefore, question 16 has 4 outcomes in its sample space.