Question

A water weed that grows fast enough to double itself in a week, is accidentally

dropped in a large lake with a surface area of 100 square kms. After 20 weeks it is

found that a quarter of the lake's surface area is under this water weed. How many

more weeks will pass before the lake surface is fully covered by the water weed ?​

Answer 1

it take 80 weeks to cover the whole lake of 100 km²