Question 94 – 2.5.3 Hypothesis test for a Normal mean (A-level only) - Questions

Environmental scientists are investigating the efficacy of a new industrial filtration plant designed to reduce lead concentrations in a local river system. They measured lead levels (in parts per billion, ppb) at 8 different sampling sites both before and after the plant became operational. The recorded concentrations are presented in the following table:

\begin{array}{|l|c|c|c|c|c|c|c|c|} \hline \text{Site} & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 \\ \hline \text{Before (ppb)} & 45.2 & 50.1 & 48.4 & 39.8 & 52.5 & 47.0 & 44.6 & 49.3 \\ \hline \text{After (ppb)} & 43.8 & 48.5 & 48.6 & 38.0 & 50.2 & 45.1 & 44.9 & 47.5 \\ \hline \end{array}

By stating your hypotheses clearly, test at the 2.5% level of significance whether the filtration plant has successfully reduced the mean lead concentration in the river. You should assume that the differences in lead levels follow a normal distribution.

\begin{array}{|l|c|c|c|c|c|c|c|c|} \hline \text{Site} & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 \\ \hline \text{Before (ppb)} & 45.2 & 50.1 & 48.4 & 39.8 & 52.5 & 47.0 & 44.6 & 49.3 \\ \hline \text{After (ppb)} & 43.8 & 48.5 & 48.6 & 38.0 & 50.2 & 45.1 & 44.9 & 47.5 \\ \hline \end{array}

2.5.3 Hypothesis test for a Normal mean (A-level only)

Question 30

2.5.3 Hypothesis test for a Normal mean (A-level only)

Question 30

2.5.3 Hypothesis test for a Normal mean (A-level only)

Question 30

2.5.3 Hypothesis test for a Normal mean (A-level only) Questions

2.5.3 Hypothesis test for a Normal mean (A-level only)

Question 30

2.5.3 Hypothesis test for a Normal mean (A-level only) Questions