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.

Question

When will a quarter of the water's surface be covered?

A.
The water's surface will be covered a quarter of the way on September 24.
B.
The water's surface will be covered a quarter of the way on September 25.
C.
The water's surface will be covered a quarter of the way on September 27.
D.
The water's surface will be covered a quarter of the way on September 26.

Answer 1

If the bacteria cover the entire water's surface on September 28 and its growth doubles every day, then we can deduce the following:

• September 28: 100% coverage
• September 27: 50% coverage (half of the surface)
• September 26: 25% coverage (a quarter of the surface)

Therefore, the correct answer is:

D. The water's surface will be covered a quarter of the way on September 26.