There are 40 doors marked with numbers 1 to 40

There are 40 doors marked with numbers 1 to 40. And there are 40 individuals marked 1 to 40. An operation on a door is defined as changing the status of the door from open to closed or vice versa. All doors are closed to start with. Now one at a time one randomly picked individual goes and operates the doors. The individual however operates only those doors which are a multiple of the number he/she is carrying. For e.g. individual marked with number 5 operates the doors marked with the following numbers: 5, 10, 15,... and 40. If every individual in the group get one turn then how many doors are open at the end?

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #70072