Psychologist Grace Arthur came up with stencil puzzles like the one above in the 1920s to test intelligence. They were used to assess children and adults until the 1950s. All you have to do is figure out how to create the square at the top by placing the available stencils on top of each other. Easy, right? Well, about 90% of adults get it wrong the first try. 

Want more? Check out the app Stenciletto, which reimagines Arthur’s test as a game.

Here’s a hint: It takes six cards to re-create the square. Luckbox found it was easier to work backwards.