MathDB
MMO 133 Moscow MO 1947 20 cubes, two materials, <=11 weighings

Source:

July 20, 2019
weighingscombinatoricsgame strategy

Problem Statement

Twenty cubes of the same size and appearance are made of either aluminum or of heavier duralumin. How can one find the number of duralumin cubes using not more than 1111 weighings on a balance without weights? (We assume that all cubes can be made of aluminum, but not all of duralumin.)