This simple math puzzle has been going viral again because it seems easy at first, yet the wording can easily catch people off guard. The question asks: “You’re in a room with 70 people. Thirty people leave, and 15 return. How many people are in the room now?” Most people immediately calculate 70 − 30 = 40, followed by 40 + 15 = 55.

However, the wording of the first sentence is where the trick comes in. It says that you are in the room “with 70 people,” which can be interpreted to mean that the 70 people are separate from you. If that interpretation is used, there are actually 71 people in the room at the beginning. The calculation would then be 71 − 30 = 41, followed by 41 + 15 = 56.

At the same time, there is another perfectly reasonable interpretation. Some people understand “you’re in a room with 70 people” to mean that the total number of people in the room, including you, is 70. Under that reading, 70 − 30 + 15 gives an answer of 55. So both answers can be defended depending on how the original wording is understood.

That is what makes this puzzle more of a reading challenge than a straightforward math problem. The numbers themselves are simple, but the phrasing encourages people to make different assumptions. It’s a fun brain teaser to share with friends and family, especially without letting anyone use a calculator. What was your first answer: 55 or 56?