Question

10. A national manufacturer of replacement shock absorbers claims that its product lasts longer than the type that the car manufacturer usually installs. To examine this claim independent samples of cars were equipped with the original (sample 1) and replacement shock absorbers (sample 2). The cars were then driven until the shock absorbers were no longer effective, and the number of kms was recorded in thousands. The 90% confidence interval for the difference in the average distance travelled was estimated as –13.47 < μ1 – μ2 < – 0.69. This indicates that

    1. there is no significant difference between the two types of shock absorber.

    2. the original shock absorber is superior to the replacement type.

    3. the replacement shock absorber is superior to the original type.

    4. both types of shock absorbers have a poor performance record.

Answer 1

The confidence interval only contains negative values. Hence,

The replacement shock absorber is superior to the original type.

Option C is correct.