Aswimming pool had 2.5 liters of water in it. some water evaporated, and then the pool only had 2 million liters of water in it. what percent of the water evaporated?

Water in the swimming pool initially = 2.5 million liters 
Water in the swimming pool after evaporation = 2 million liters 
Therefore, volume of water evaporated = 2.5 million liters - 2 million liters 
 =0.5 million liters 
To find the percent of water evaporated, divide the volume of water evaporated by the volume of water in the swimming pool initially and then multiply it by 100. 
 Percent of water evaporated =( 0.5 / 2.5) x 100  =20%