Math & Logic · Ages 18+
Riddle #212
Imagine a rope tied snugly around the Earth's equator. You add exactly one metre to its length, then lift it so it stands the same height above the ground the whole way round. Roughly how high off the ground is it?
You solved this one before
Answer: About 16 centimetres — enough to slide your hand under.
Circumference is 2πr, so adding 1 m of rope raises the radius by 1 ÷ 2π ≈ 0.159 m. The size of the Earth cancels out completely — the answer is identical for a rope around a tennis ball.