A team of environmental scientists measures the concentration of a specific pollutant (in parts per million, ppm) emitted by eight industrial catalytic converters before and after a specific chemical cleaning process. The emission levels are assumed to be normally distributed. The results for the eight converters are shown in the table below:

Converter	$C_1$	$C_2$	$C_3$	$C_4$	$C_5$	$C_6$	$C_7$	$C_8$
Before	42.5	38.8	45.2	40.1	39.5	41.4	43.6	37.9
After	41.3	37.0	43.7	38.0	38.1	39.7	41.7	36.7

Calculate a 98% confidence interval for the mean difference in pollutant emissions.

Use your confidence interval to determine whether there is evidence of a change in the mean pollutant emissions. State your hypotheses clearly and provide a reason for your conclusion.

Converter	$C_1$	$C_2$	$C_3$	$C_4$	$C_5$	$C_6$	$C_7$	$C_8$
Before	42.5	38.8	45.2	40.1	39.5	41.4	43.6	37.9
After	41.3	37.0	43.7	38.0	38.1	39.7	41.7	36.7

Calculate a 98% confidence interval for the mean difference in pollutant emissions.

Use your confidence interval to determine whether there is evidence of a change in the mean pollutant emissions. State your hypotheses clearly and provide a reason for your conclusion.

2.5 O: Statistical hypothesis testing

Question 35

Markscheme

2.5 O: Statistical hypothesis testing

Question 35

Markscheme

2.5 O: Statistical hypothesis testing

Question 35

2.5 O: Statistical hypothesis testing Questions

2.5 O: Statistical hypothesis testing

Question 35

2.5 O: Statistical hypothesis testing Questions