One filter decreases the concentration of harmful substances in water by half. If water that contains less than 0.1 percent of harmful substances is considered clean, how many filters are required to clean 200 liters of water containing 0.5 liters of harmful substances ?
Choose the correct option
A) 2 B) 3 C) 5 D) 6 E) 8
Initially, the concentration of harmful substances in the water is 0.5/200∗100%=0.25%. One filter will reduce this concentration to 0.125%. Two filters will reduce the concentration to 0.0625% which is less than 0.1%   2nswer: 2
<result>A</result>
One filter decreases the concentration of harmful substances in water by half. If water that contains less than 0.1 percent of harmful substances is considered clean, how many filters are required to clean 200 liters of water containing 0.5 liters of harmful substances ?