First, determine the amount of water that evaporated by subtracting the final volume of water in the pool from the initial volume. That is,
V, evaporated = 2.5 million liters - 2 million liters
V, evaporated = 0.5 million liters
Then, to determine the percentage of water evaporated, we divided the amount of water evaporated by the original amount and multiply the quotient by 100%.
P = (0.5 million liters)/(2.5 million liters) x 100%
P = 20%
Answer: 20%