The Equator is about 40,075 kilometres (24,901 miles) long. About 78.7% lies across water and 21.3% over land but, for the purposes of the game, we are going to assume that it is possible to walk all the way.

Normal walking speed is about 5 km per hour (a little over 3 mph) and we're not allowing rest breaks. So a simple division gives you (approximately) 8,000 hours. That's about 333 days or 11 months.

But, what if you were dawdling, say, at 3 km per hour (under 2 mph)? Your time would go up to about 555 days: that's a bit over eighteen months, but nowhere close to the option listed of 5 years.

But, perhaps you are thinking of sports walkers who can manage amazing speeds of 14 km per hour (8.7 mph) over short distances? If you could keep that fast pace up, the journey would take you about 120 days: that's around four months and well above the option listed of two months.

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