Answer: 33
Explanation:
From the question, a trial of 10 filters shows the effective days of each filter to be 94, 101, 120, 87, 93, 91, 105, 92, 91, and 100.
The range of effective days of the trial water filters will be the difference between the highest number given and the smallest number given.
Highest number = 120
Lowest number = 87
Range = 120 - 87 = 33