Quick & curious · Numbers

When things double, your gut gets it badly wrong.

A moorhen swims among water-lily leaves and pink flowers
Photo: Toby Hudson · CC BY-SA 3.0 · Original

48daysuntil the whole lake is covered

Your guess

Lily pads double daily, after 48 days the lake is covered. When was it half covered?

More about it

The puzzle is part of Shane Frederick's Cognitive Reflection Test (2005). It measures whether you question the first answer that comes to mind – or just say it. The original test had only three questions.