Scientists need to be able to detect small amounts of contaminants in the environment. As a check on current capabilities, measurements of lead content( μ g / L) are

taken from twelve water specimens spiked with a known concentration. (courtesy

of Paul Berthouex). 

2.4 2.9 2.7 2.6 2.9 2.0 2.8 2.2 2.4 2.4 2.0 2.5

The data has  and . Calculate the test statistic correct to two decimal places.