MathDB
2018-2019 Fall OMO Problem 6

Source:

November 7, 2018
Online Math Open

Problem Statement

Patchouli is taking an exam with k>1k > 1 parts, numbered Part 1,2,,k1, 2, \dots, k. It is known that for i=1,2,,ki = 1, 2, \dots, k, Part ii contains ii multiple choice questions, each of which has (i+1)(i+1) answer choices. It is known that if she guesses randomly on every single question, the probability that she gets exactly one question correct is equal to 20182018 times the probability that she gets no questions correct. Compute the number of questions that are on the exam.
Proposed by Yannick Yao