Question

Bacteria begins to grow on the water's surface in a non-operational swimming pool on September 20. The bacteria grows and covers the water's surface in such a way that the area covered with bacteria doubles every day. If it continues to grow in this way, the water's surface will be entirely covered with bacteria on September 28. When will a quarter of the water's surface be covered?

Answer 1

Working backwards, on Sept 27 the pool will be half covered, and on Sept 26 the pool will be one quarter covered.