The pH scale measures the acidity or alkalinity of a solution. Water samples from different locations and depths of a lake usually have normally distributed pH values. The mean of those pH values, plus or minus one standard deviation, is defined to be the pH range of the lake.
Lake Fishbegon has a pH range of 5.8 to 7.2. Sketch the normal curve, and shade those portions that are outside the pH range of the lake.