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Compute probability last passenger gets own seat

Last updated: Mar 29, 2026

Quick Overview

This question evaluates a candidate's understanding of probability theory, combinatorics, and reasoning about sequential random processes, with emphasis on symmetry and conditional dependence.

  • medium
  • Schonfeld
  • Coding & Algorithms
  • Data Scientist

Compute probability last passenger gets own seat

Company: Schonfeld

Role: Data Scientist

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Take-home Project

There are 100 passengers boarding a plane with 100 seats, numbered 1 to 100. Passenger `i` (for 1 ≤ i ≤ 100) has a ticket for seat `i`. The boarding process is as follows: 1. Passenger 1 is drunk and ignores the seat assignment. They choose **one of the 100 seats uniformly at random** and sit there. 2. For each subsequent passenger `k` from 2 to 100: - If seat `k` (their assigned seat) is still empty, they sit in seat `k`. - Otherwise (if their assigned seat is already occupied), they choose **uniformly at random** from all the remaining empty seats and sit in one of those. You are passenger 100. What is the probability that you end up sitting in your **own assigned seat** (seat 100)? Give the final probability as a simplified fraction or decimal.

Quick Answer: This question evaluates a candidate's understanding of probability theory, combinatorics, and reasoning about sequential random processes, with emphasis on symmetry and conditional dependence.

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Schonfeld
Nov 1, 2025, 12:00 AM
Data Scientist
Take-home Project
Coding & Algorithms
1
0

There are 100 passengers boarding a plane with 100 seats, numbered 1 to 100. Passenger i (for 1 ≤ i ≤ 100) has a ticket for seat i.

The boarding process is as follows:

  1. Passenger 1 is drunk and ignores the seat assignment. They choose one of the 100 seats uniformly at random and sit there.
  2. For each subsequent passenger k from 2 to 100:
    • If seat k (their assigned seat) is still empty, they sit in seat k .
    • Otherwise (if their assigned seat is already occupied), they choose uniformly at random from all the remaining empty seats and sit in one of those.

You are passenger 100. What is the probability that you end up sitting in your own assigned seat (seat 100)?

Give the final probability as a simplified fraction or decimal.

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