Puzzles
The Cognitive Reflection Test's Jerry puzzle
Jerry took a test along with the rest of his class. When the marks came back, it turned out Jerry had scored the 15th highest mark in the class - and also the 15th lowest mark in the class. How many students are in Jerry's class?
Reveal the answer
29. The tempting fast answers are 30 (15+15) or 15, but both are wrong: 14 students scored above Jerry and 14 scored below him, and adding Jerry himself gives 14+14+1=29. This is one of four new items added in a 2014 'CRT-2' expansion of Shane Frederick's original three-question Cognitive Reflection Test (the one with the famous bat-and-ball problem), created because the original questions had become so well known that many test-takers simply recalled the answers instead of reasoning through them.