CS109: Probability for Computer Scientists
Winter 2026
Monday, Wednesday, Friday 3:00pm - 4:20pm in-person in Hewlett 200

Week 5 TODO

Finish PSet4
Go to Midterm PEP
Study for the Midterm

Teaching Team

Instructor:
Juliette Woodrow
Juliette

Awesome TAs: cs109 @ cs.stanford.edu

This Week in CS109
Date Lecture Outside Class
Mon, Feb 2nd General Inference PEP Starts!
Wed, Feb 4th Multinomial Last day of PEP.
Fri, Feb 6th Beta Distribution PSet 4 Due.
Midterm Exam Logistics
2026020615

The CS109 midterm exam will be Tuesday, February 10th from 7-9pm. It is a 2-hour, closed book, closed calculator/computer exam. You are, however, allowed to bring 3 pages (front and back) of notes in the exam, formatted in any way you like. Make sure to practice before the exam.

You can find more information about the midterm on the Midterm Handout. The midterm will cover all material from lectures 1-13 and problem sets 1-4. We will have a review session on Friday, February 6th from 4:30-5:30pm in Shriram 104. We hope to see you there!

Bishop Auditorium:
Last names beginning with A-L

Building 420-040:
Last names beginning with M-Z

Pset 4: Models
2026013015

Problem Set #4 has been released. Practice more with inference and probabilistic models. PSET4 is due Feb 6th. This is the last problem set before the midterm.

Sign Up for Personalized Exam Prep (PEP)
2026012615

PEP for the midterm is next week! PEP ("Personalized Exam Prep") is a one-on-one 15-minute meeting you have with a TA in the week before the midterm (you will have another one the week before the final as well!). PEP is designed to help you figure out how to best prepare for exams. In prior quarters, students found PEP to be super helpful, so we hope you'll think so too!

Sign up for PEP here: PEP Signup Form Sign ups are first come, first served so sign up asap to get your favorite time. Check out the Ed post on PEP for FAQs.

Pset 3: Random Variables
2026012315

Problem Set #3 has been released. On PSet 3 you will practice working with continuous random variables. Problems 1-8 can be completed after Friday's lecture and problem 9 can be completed after Monday's lecture.

Pset 2: Discrete Random Variables
2025100315

Problem Set #2 has been released! It features the discrete random variables we've learned in class -- you'll analyze a bloom filter (a probabilistic datastructure), tell the difference between true randomness and a human faking it, and learn about exponential backoff!

Section + Theme Song
2026010915

Sign up for section using the Section Sign up Form before Sunday Jan 11th at 5pm. Suggest songs for the class playlist (also by 5pm on Sunday).

Pset 1: Core Probability
2026010715

Problem Set #1 has been released! It is due on Friday, Jan 16th at 10:00pm Pacific. Practice working with conditional probability, independence, and Bayes' Theorem. Problems 1, 2, 3, 7 and 8 can be done with Wednesday's lecture material and the rest of the problems can be completed after Friday's lecture.

Welcome

Welcome to CS109! We are looking forward to an uplifting and exciting quarter. Class starts Monday, Jan 5th at 3pm PT in Hewlett 200. See you there 🌱.

Getting Started in CS109

The Syllabus page has details on course logistics.
The Honor Code handout describes how the Honor Code applies in the context of the work you will do in CS109.
The Schedule page has a list of all topics that we will cover in CS109, the lecture schedule, and the problem set dates and deadlines.
The Office Hours page has contact information for the teaching team. Office Hours will be listed on this calendar and start on Wednesday, Jan 7th.
Section enrollment details will be released on the first day of class; you do not enroll in section via Axess.


RESOURCES

Discussion
Course Reader
Syllabus
Schedule
Office Hours

Key Dates

Midterm: Feb 10th, 7p
Final: Mar 17th, 8:30a
Last lecture: Mar 13th

Course Values

Everyone is welcome. Intellectual joy. Be kind. Be humane. Social connection. Learn by doing. Thrill of building. Adapt to new contexts.
CS109: Probability for Comp. Science
Winter 2026, MWF 3:00pm - 4:20pm, Hewlett 200

Week 5 TODO

Finish PSet4
Go to Midterm PEP
Study for the Midterm

Teaching Team

Instructor: Juliette Woodrow

RESOURCES


Key Dates

Midterm: Feb 10th, 7p
Final: Mar 17th, 8:30a
Last lecture: Mar 13th

Announcements

This Week in CS109
Date Lecture Outside Class
Mon, Feb 2nd General Inference PEP Starts!
Wed, Feb 4th Multinomial Last day of PEP.
Fri, Feb 6th Beta Distribution PSet 4 Due.
Midterm Exam Logistics
2026020615

The CS109 midterm exam will be Tuesday, February 10th from 7-9pm. It is a 2-hour, closed book, closed calculator/computer exam. You are, however, allowed to bring 3 pages (front and back) of notes in the exam, formatted in any way you like. Make sure to practice before the exam.

You can find more information about the midterm on the Midterm Handout. The midterm will cover all material from lectures 1-13 and problem sets 1-4. We will have a review session on Friday, February 6th from 4:30-5:30pm in Shriram 104. We hope to see you there!

Bishop Auditorium:
Last names beginning with A-L

Building 420-040:
Last names beginning with M-Z

Pset 4: Models
2026013015

Problem Set #4 has been released. Practice more with inference and probabilistic models. PSET4 is due Feb 6th. This is the last problem set before the midterm.

Sign Up for Personalized Exam Prep (PEP)
2026012615

PEP for the midterm is next week! PEP ("Personalized Exam Prep") is a one-on-one 15-minute meeting you have with a TA in the week before the midterm (you will have another one the week before the final as well!). PEP is designed to help you figure out how to best prepare for exams. In prior quarters, students found PEP to be super helpful, so we hope you'll think so too!

Sign up for PEP here: PEP Signup Form Sign ups are first come, first served so sign up asap to get your favorite time. Check out the Ed post on PEP for FAQs.

Pset 3: Random Variables
2026012315

Problem Set #3 has been released. On PSet 3 you will practice working with continuous random variables. Problems 1-8 can be completed after Friday's lecture and problem 9 can be completed after Monday's lecture.

Pset 2: Discrete Random Variables
2025100315

Problem Set #2 has been released! It features the discrete random variables we've learned in class -- you'll analyze a bloom filter (a probabilistic datastructure), tell the difference between true randomness and a human faking it, and learn about exponential backoff!

Section + Theme Song
2026010915

Sign up for section using the Section Sign up Form before Sunday Jan 11th at 5pm. Suggest songs for the class playlist (also by 5pm on Sunday).

Pset 1: Core Probability
2026010715

Problem Set #1 has been released! It is due on Friday, Jan 16th at 10:00pm Pacific. Practice working with conditional probability, independence, and Bayes' Theorem. Problems 1, 2, 3, 7 and 8 can be done with Wednesday's lecture material and the rest of the problems can be completed after Friday's lecture.

Welcome

Welcome to CS109! We are looking forward to an uplifting and exciting quarter. Class starts Monday, Jan 5th at 3pm PT in Hewlett 200. See you there 🌱.

Getting Started in CS109

The Syllabus page has details on course logistics.
The Honor Code handout describes how the Honor Code applies in the context of the work you will do in CS109.
The Schedule page has a list of all topics that we will cover in CS109, the lecture schedule, and the problem set dates and deadlines.
The Office Hours page has contact information for the teaching team. Office Hours will be listed on this calendar and start on Wednesday, Jan 7th.
Section enrollment details will be released on the first day of class; you do not enroll in section via Axess.


Course Values

Everyone is welcome. Intellectual joy. Be kind. Be humane. Social connection. Learn by doing. Thrill of building. Adapt to new contexts.