Cooper 11 0 26 A lake has a volume of 10 8m 3 A river flows into the lake at the rate of 4 X 10 5m 3 day The same amount of pure water evaporates from the lake each day so the volume of the lake does not change The river contains 5 pollution The lake is initially unpolluted a What is the percentage pollution in the lake after t days b When does the pollution in the lake reach 1 after days