12.89 An industrial sales manager, testing the effectiveness of three different sales presentations, randomly selected a presentation to be used when making the next sales call on 14 customers. The numbers of units purchased as a result of each sales call are shown here. Use the 0.05 level in determining whether the three sales presentations could be equally effective. (Use data file XR12089.)

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Presentation 1 2 3 7 13 14 9 10 15 11 11 12 7 13 10 14 13