Here's a quick brain-stretcher: over a certain period, rain fell on 11 days. A morning rain was always followed by a clear afternoon. An afternoon rain was always preceded by a clear morning. A total of nine mornings and 12 afternoons were clear. How many days had no rain at all? Would the answer be two, three, four or five days?
Such puzzles don't faze students who took part in the South East Asian Mathematics Competition (Semac) in Bangkok last weekend. The Hong Kong contestants included a contingent of six students from the French International School - Edwina Gautier, Michelle Kempis, Helena Kwon, Sally Nakai, Jean Baptiste Rioual and Linda Woodrow - led by maths teacher Swati Ray.
The students had committed time out of class to prepare for this event and looked forward to tackling similar problems with teams from other international schools in the region.
In my experience as form tutor, students seldom use the words "excitement" and "mathematics" in the same sentence. So, the competition is a valuable platform for livening up maths.
"First of all, students see that maths can be fun, and devoting a weekend to solving maths problems is not daunting," Ray says. "Second, the different events help them understand the practical application of mathematics. And last but not the least, students learn from their peers. They are empowered and motivated when they see students their age attack problems they are not able to."
Semac was started in 2001 by Steve Warry, a teacher at the Alice Smith School in Kuala Lumpur, who believed that maths could be a "spectator sport". Hong Kong students have been enthusiastic participants from the start and have placed in the top three almost every year.
Every event in the competition features five common rounds, with the host country adding bespoke rounds based on resources available. The five common bouts consist of two individual multiple-choice papers, a team question paper, a carousel of practical team activities and an energiser round. While there is a spirit of healthy competition, the emphasis is on befriending students from other schools through the buddy team rounds.
The recent weekend brought in many high-profile mathematicians, including Johnny Ball, Marcus du Sautoy, and Andrew Jeffery, who have helped fuel students' enthusiasm for mathematics.
Why don't more students enjoy maths? Ray, who has been teaching the subject for nearly two decades, reckons youngsters' apprehension often stems from the way they handle difficult topics: "Students often stop taking risks and then lose their resolve when they encounter a problem."
With other subjects, they may be able to avoid having to comprehend the difficult stumbling block. But not in maths, which is based on a scaffolding of various concepts, Ray suggests.
Many students don't see much use for maths in their lives (apart from being able to count), and question the relevance of such tools as learning matrices, Venn diagrams and derivatives. However, Ray says they should remember how studying maths builds critical thinking skills.
"Maths develops the ability to make connections and see patterns, which are lifelong skills that students need for other subject areas."
That's why maths is a mandatory subject for the IB Diploma and the new Hong Kong Diploma of Secondary Education, unlike some school certificates that let students drop the subject after Year 10.
Ray concedes arithmetic drills in after-school programmes such as Kumon and Sylvan can help students speed up their calculation which, in turn, supports learning in other areas of maths.
But she says "they are not a substitute for developing problem-solving skills, and are only useful if students comprehend the underlying concepts before undertaking repetition".
By the way, for those who persisted with the brain-teaser, five days had no rainfall.
Anjali Hazari teaches IB and IGCSE biology at the French International School