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12.2    For each of the following situations, identify the response variable and the populations to be compared, and give I, the pf, and N.

(a)    A company wants to compare three different water treatment devices that can be attached to a kitchen faucet. From a list of potential customers, they select 225 households who will receive free samples. One-third of the households will receive each of the devices. The household is asked to ratę the likelihood that they would buy this kind of device on a 5-point scalę.

(b)    The strength of concrete depends upon the formula used to prepare ' ,,It. One study compared five different mixtures. Six batches of each

mixture were prepared, and the strength of the concrete madę from each batch was measured.

(c)    Which of three methods of teaching statistics is most effective? Twenty students are randomly assigned to each of the methods, and their scores on a finał exam are recorded.

12.3    Refer to Exercise 12.1: For each situation, give the following:

(a)    Degrees of freedom fó’r the model, for error, and for the total.

(b)    Nuli and altemative hypotheses.

(c)    Numerator and denominator degrees of freedom for the F statistic.

12.4    Refer to Exercise 12.2. For each situation, give the following:

(a)    Degrees of freedom for the model, for error, and for the total.

(b)    Nuli and altemative hypotheses.

(c)    Numerator and denominator degrees of freedom for the F statistic.

12.5    An experiment was run to compare three groups. The sample sizes were 10, 12, and 14, and the corresponding estimated standard deviations were 18,

24, and 20.