Question

The Water Department checks the city water supply on a regular basis for

contaminants such as lead. The Water Department takes 200 samples and
estimates that the concentration of lead in your drinking water is 3.2 ppb
(parts per billion), with a standard deviation of 0.3 ppb.
Assuming the samples were random and unbiased, how much confidence
can you have in this data?

Answer 1

99.7% confident the average concentration of PCBs in the water supply is between 2.3 ppb and 4.1 ppb

Explanation:

A P E X Confirmed

Answer 2

The correct answer is: 95% confident the average concentration of PCBs in the water supply is between 2.4 ppb and 3.6 ppb.

Explanation: