One question describes a "digital snail" that leaves a trail of binary numbers.
Another asks for help in decoding a three-character password, using a string of numbers and letters.
These are two of the 14 questions seen in a service 96 double-decker bus, which runs through the National University of Singapore.
The experience, called #ChallengeInTransit, is a collaboration between Tower Transit Singapore (TTS), which runs the service, and defence research and development organisation DSO National Laboratories. It started on Jan 15 and will run till end March.
Answers must be submitted through the website curiousbus.sg, which also features the questions in full.
Participants who answer one question correctly stand a chance to win a Hubsan X4 Drone, which is worth about $100.
The challenge "creates an interesting journey for passengers", said TTS group communications director Glenn Lim.
For DSO, the campaign is a part of the company's recruitment efforts.
Ms Serene Tan, 46, DSO's director of the human resource and communications division, said: "We were looking for innovative ways to shed some light on science and engineering, as well as what DSO does, to the public."
There are currently no plans for the participants' information to be used, but Ms Tan said DSO is on the hunt for physicists, chemists and computer science majors.
To that end, the questions cover topics such as science and cyber security.
Next to the questions are the profiles of the DSO engineers, researchers and scientists who created the questions.
Mr Gabriel Ng, 31, came across the questions through a friend a few weeks back. The civil servant, who enjoys solving puzzles, submitted answers for three of the questions.
"It is interesting, and it is a good way to look for candidates who are interested in the field but may not have any formal training," Mr Ng said.