SS 2857 - Announcements

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Last updated December 6, 2017, 1:30pm

1. 1)Most of you had the following problem on Quiz 1: If P(A) = 0.7 and P(B) = 0.9 find

the largest possible value of P(AuB) - P(AnB).

Many solutions went roughly like this: We always have P(AuB) <= 1, thus

P(AuB) - P(AnB)  <= 1- P(AnB). Next, we have P(AnB) >= 0.6 since we need to

have minimum “overlap” between A and B. Thus, P(AuB) - P(AnB) <= 1 - 0.6 = 0.4

and this is the maximum possible value.

While this approach gives the correct answer in this case, it is wrong. To see this, let us try

it one more time with different numbers. Let P(A) = 0.2 and P(B) = 0.3. Then we still have

P(AuB) <= 1 and this time P(AnB) >= 0. Thus, P(AuB) - P(AnB) <= 1 - 0 = 1.

Unfortunately, now we get a wrong answer since value 1 can never be achieved

for P(AuB) - P(AnB).

The correct approach is to use the formula P(AuB) - P(AnB) = P(A) + P(B) - 2 P(AnB)

and then minimize P(AnB). So, for the second example, the correct answer is 0.2+0.3 - 2*0 = 0.5.

2) Request for a Volunteer Note Taker

Hello Students,

There are one or more students in your class with a condition that restricts their ability to write comprehensive lecture notes. The student(s) would benefit from having a set of lecture notes written by another student, so that they could check the notes that they have written and see if they are accurate and complete. In some cases, your notes might be used to assist a student who has had to miss class because of their disability. If you take good notes and you would like to help out, please send an email to peernotes@uwo.ca indicating that you saw this message and want to volunteer. You could be eligible to receive a letter of acknowledgement indicating that you assisted a student with a disability as a volunteer note taker at Western, and/or other rewards.

1. 3)About the upcoming exam. The midterm is going to include

1. a)The first 48 pages of the course notes

2. b)The first two homework sets.

3. c)The first five tutorials.

Nothing outside of these three sources will be on the midterm.

Know the definitions and the statements of the results (theorems, propositions, lemmas, etc. if any) Know all major fomulas. (There will be no formula sheet for the midterm, only for the final exam.) Learn how to use proper notation.

If you work with an event make sure you explain what this event is.

4) Dr. Sendov’s office hour on Wed Dec 5, 2017 is cancelled due to illness.

5) Example 212 in the course notes has to be recalculated to take into account continuity correction.