I want to choose a list of different numbers from the first 20 positive integers so that no two of my numbers differ by 5. (a) What is the largest value of for which this is possible? (b) How many different lists are there with this many numbers?
Sign in or create an account to reveal answers, view the solution, and save your progress. Create a free account to unlock practice and keep track of your work.
Junior Mathematical Olympiad 2009 (2009)
One puzzle per day. Cryptarithm, Magic Square, Summit. No sign-up required to play.
Play daily puzzle →Interactive problems and curated lessons—water pouring, magic squares, knight's tour, and more.
Browse library →See how you rank. Top solvers by problems solved correctly. Sign in to climb the ranks.
View leaderboard →Junior Mathematical Olympiad 2009 (2009)