This turned out to be one of those problems were you could begin working from th e start of the race or work backwards from the end of the race. However, you don't end up with exactly the same answer! This is because of a slight mismatch in the information you are given to work with. If you start with 2km (2 000 meters) and start halving it, it doesn't exactly make 1 metre at the end (0.98 m). Because the problem does state that it ends exactly 1 metre from the end, it's tidier start with that and double - but then you end up a bit over the 2 kilometres. If you assume that the runner was not able to measure time and distance exactly while running, then it seems fine to accept an approximate answer. It turns out that the practice race is about 4 kilometres and it took about 2 hours.

Here are the figures that Rowena Scott came up with:

"On practise run, the race was 4096 metres, and it takes two hours for Chandrika to do the long distance run.

First of all, I thought Chandrika ran 2000m, then jogged 1000m, then walked 500m, then 125, then 62.5m and I thought that there wouldn't be exactly one metre left.

If there was 1 metre left, she could have travelled 1m, 2m, 4m, 8m, 16m, 32m, 64 m, 128m, 256m, 512m, 1024m, 2048m.

If you add all these distances, you get 4096m. There are 12 lots of distance, 12 x10=120mins=2hours."

Daniel Loh (Age 10, Anglo-Chinese School, Singapore) used the 'working backwards' method and got the same results except he included the final 10 minutes in the time.

Owen Cox & Ian Corner (Age 9, Crofton Junior School, Kent) built up a table. With a little rounding up of the numbers you see that it comes out very close to 4km in 2 hours.