Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: THEend8_
Instructions
1. There are 8 questions and a total of 40 marks. Attempt as many as you can.
2. Show all of your work and fully explain your reasoning. Cite any results from the
textbook or lectures that you use.
3. Upload your solutions to Gradescope by May 13, 10:00am PST.
4. Please ensure that:
— all uploaded files are clearly readable
— every part of every question is on a separate page
— all files are in the proper order.
5. If DSP, you may instead email your solution to your GSI by May 13, 10:00pm PST if
150% time or by May 14, 10:00am PST if 200% time.
6. You MUST upload a declaration of academic honestly, as described below. Your
exam will not be accepted otherwise.
Academic honesty
Your exam will be accepted ONLY IF you include a declaration of academic honesty.
1. In your own writing, copy out ALL of the following statements:
— As a member of the UC Berkeley community, I act with honesty, integrity, and respect
for others.
— I will not communicate with anyone about the exam, besides the instructor and GSIs
for the entire duration of the exam period.
— I will not refer to any books, notes, or online sources of information while taking the
exam, other than the course textbook, lecture notes and other materials available on
the official STAT 134 webpages.
— I will not take screenshots, photos or otherwise make copies of exam questions.
2. Sign your name.
3. Upload this document to Gradescope together with your solutions.
Page 1 of 3
1. [2 marks] Suppose that X and Y are independent standard normal random variables.
Using rotational symmetry, show that P(Y > √
3|X|) = 1/6.
Hint: Recall arctan(√
3) = π/3.
2. [5 marks] Every day a professor leaves their home in the morning and walks to their
office. Every evening they walk home. They take their umbrella with them only if it is
raining. If it is raining and they do not have their umbrella with them (at their home
or office), then they must walk in the rain. Suppose that it rains with probability
1/3 at the beginning of any given trip independently of all other trips. Show that
63/16 ≈ 4 is the expected number of days until the professor must walk in the rain
without their umbrella (either that morning or evening), supposing that initially they
have their umbrella with them at home.
Hint: Let μ be the expected number of days supposing they initially have their umbrella
with them at home, and let ν be the expected number of days supposing that they do
not. Explain why
and then, similarly, find an equation for ν in terms of μ and μ. Use these equations to
solve for μ.
3. In a large class, the midterm and final exam scores (M, F) are approximately bivariate
normal with μM = 60, σM = 25, μF = 65, σF = 20 and ρ =√3/2.
(a) [2 marks] Explain why 65 + 4ρ the expected final exam score of a student whose
midterm score is 65.
(b) [3 marks] Using Φ(1) ≈ 0.84, find the conditional probability that this student’s
final exam score is at least 75+4ρ (that is, at least 10 points higher than expected)
given that their midterm score is 65.