Notes and puzzles are a staple in Dying Light: The Beast, and the more you explore Castor Woods, the more you’ll find. The ‘Experiment on the Infected’ note is one such note that’s tied to a puzzle that requires a bit of mathematical proficiency. However, the solution is incredibly simple; all it requires is a bit of brainstorming and UV light. Here’s what you need to do to solve the ‘Experiment on the Infected’ note in Dying Light: The Beast.
Solving the ‘Experiment on the Infected’ Note

The solution for the safe in the Infected Experiment Chamber is 15-22-40. First, you need to find the ‘Experiment on the Infected’ note, which is in the building next to the Green Hotel in the Old Town in Dying Light: The Beast. The area is shown in the map above.
Once you reach there, the location will be marked with a Golden Treasure Chest icon. Use your Survival Instincts and locate a window or a door behind the hotel. Use it to access the building, and you’ll instantly come across a whiteboard, two deceased zombies, and the ‘Experiment on the Infected’ note with the safe beside it.
Read the note to find out that the person who wrote the note wanted to test out the advanced cognitive skills of the two dead zombies and created a mathematical test on the whiteboard using some arithmetic operations and UV light. Now, what you need to do is use your UV light and shine it on the whiteboard to find the clues to the puzzle.

As soon as you shine the UV light on the whiteboard, you’ll get three mathematical problems that you must solve to open the safe:
- 25 – 10 = 15
- 11 * 2 = 22
- 51 – 11 = 40
and you have to input them in order. Now that you’ve expressed your mathematical proficiency flawlessly and obtained the code, head to the safe beside the ‘Experiment on the Infected’ Note, and use it to unlock the safe.
For your mindboggling troubles, you’ll be rewarded with the Puff Weapon Mod, which will be available to craft at any Workbench in the game. This Weapon Mod adds Blast to some of the weapons in your arsenal, making you more well-equipped to deal with the deadly threats in Castor Woods.
That’s all you have to do to solve the ‘Experiment on the Infected’ note puzzle in Dying Light: The Beast. Since you’re already inside the Old Town, check out our comprehensive guides on the Last Wish sidequest and the Orange Hotel safe solution to get more valuable loot in your journey.

