Today’s featured puzzles are designed to challenge readers’ engineering knowledge and critical thinking abilities. Adapted from the newly released book How to Keep a Plane in the Sky by technology reporter Alex Davies, the questions explore fascinating aspects of test engineering and the scientists who ensure structural integrity in everyday objects.
The first puzzle presents a scenario at a cranberry sorting facility, where thousands of berries are dropped onto a board each minute. Since firm, good cranberries bounce while soft, spoiled ones do not, solvers must identify the simple method used to separate the viable fruit from the rest.
A second question addresses the design of child-resistant medicine bottle caps in the United States. Despite appearing overly secure, these caps are only required to deter 85% of children under the age of five. Readers are asked to explain why regulators do not aim for a higher percentage of prevention.
The third challenge examines the 2020 replacement of the Golden Gate Bridge’s pedestrian handrail. Engineers swapped the old H-shaped metal balusters for thin vertical slats to reduce wind resistance and improve safety during storms. However, this change led to two significant unintended consequences that participants must identify.
Finally, the set includes a historical question regarding aircraft cabin pressure. In the early 1950s, UK manufacturer de Havilland faced mid-flight fuselage failures with its Comet jet, the world’s first commercial airliner. The puzzle asks how engineers managed to pressure-test the aircraft without taking it into the air.
Solutions to these riddles will be published at 5 pm UK time. In the meantime, readers are encouraged to discuss their favorite engineering anecdotes rather than revealing answers.
The puzzle column is authored by Alex Bellos, who recently announced he has been awarded the 2026 Christopher Zeeman Medal. Presented by the London Mathematical Society and the Institute for Mathematics and Its Applications, the medal is the UK’s most prestigious honor for mathematics communication. Belros has been contributing these alternating Monday puzzles since 2015.
Davies’ book highlights the stories behind the testing processes that prevent objects from cracking, breaking, or exploding, offering insight into the rigorous standards that underpin modern engineering trust.
Love how these puzzles show the hidden engineering in everyday objects. Truly fascinating stuff.
Why stop at five? Elderly people can’t open those bottles either, honestly it’s frustrating.
Alex Bellos is a legend. Can’t wait to see if I nailed the cranberry sorting one.
Those Golden Gate Bridge handrails sound like a recipe for disaster waiting to happen.
I never knew about the 85% rule for child-proof caps. Mind blown!