Q. In the Olympic Stadium, what are the black square things you can see in front of spectators? Janet King
A. They're LED light boards. They were used in the opening ceremony to light up the stands – you can pick them up to wave about. They're unlit during the athletics, so they're left attached to the seat in front of each person. Hence your accurate description of "black square things".
Q. In some races, it appears at least half the field are wearing yellow shoes! When did this become a trend, and why? What's so special about yellow? Laura Akerman
A. The competition at the Olympics isn't confined to sport. The marketing battle between Nike and Adidas is intense, as the German firm tries to close the gap on the world leader (Nike's annual sales stand at around $21bn, against $17bn for Adidas). Hence Adidas are supplying 41 different types of footwear to Olympic athletes to try and grab the world's attention, and there's no point keeping that to themselves, so the trainers tend to be in the most eye-catching colour possible. What next for the Rio Games? Who knows – maybe we'll see a whole new colour invented that's visible from space.
Q. So China and the US are top of the medals table – but they have the most people to choose from. Who would win by head of population? S Wardle
A. Slovenia (2 million people; one silver, three bronzes) were doing well, as were Cyprus (just over 1 million people; one silver). But then Kirani James won the men's 400m and Grenada rose to top spot – only one medal, a gold, but from a population of 110,000, they'll be hard to beat.
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