Question

Fresh water from rivers and lakes varies in acidity/alkalinity depending on the rocks and soils it runs over. Granite country yields water that is slightly acidic, while water from limestone country is slightly alkaline. Acidity and alkalinity are measured on a pH scale, on which 7 is neutral, values below 7 are acidic and values above 7 are alkaline. pH can change due to pollution or due to waste from biomass such as algae.

A certain river, fed by various tributaries, usually has a pH of about 6.4 (a bit acidic). The data below shows pH values from randomly-selected sites on this river and its tributaries.

pH
5.7
5.7
5
5.8
4.6
4.7
4.7
5.4
5.9
6
5.4
5.9
5.3
5.8
6
5.3
5.2
5.8
5.5
5.9
5.6
6.3
6.4
6.5
6.6
6.1
6.3
6.9
6.7

(a) Provide a graph of the data distribution. Bear in mind that distribution shape and outliers may be important. [4 marks]

(b) How much evidence is there that the pH of water in this river system has changed?
Evaluate the evidence using a hypothesis test with a significance level of 1%. Take care to state and evaluate all assumptions, and provide an appropriate conclusion. [11 marks]

(c) Provide a 99% confidence interval for the mean pH in this river system. [3 marks]

Answer 1

ANSWER

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