"On practice run, the race was 4095 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 4095m. There are 12 lots of distance, 12 x10=120mins=2hours."
Daniel from 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 and Ian from 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.
|Minutes||Minutes so far||Distance in metres||Distance so far|
|10||10||2 000.00||2 000.00|
|10||20||1 000.00||3 000.00|