19. The chlorine value must be within 1.75 ppm, which means that the chlorine must be +/- 1.75 ppm from 3.25 ppm. This gives us a range of 1.5 to 5.
a. 1.5 ≤ | x | ≥ 5
The chlorine, represented by x, in ppm, must be equal to or between those two values.
b. He should add more chlorine because 1.0 ppm is less than 1.5 ppm, so it is not in the range for the safe level of chlorine.
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