A large company buys thousands of light bulbs every year. The company is currently considering four brands of light bulbs to choose from. Before the company decides which light bulbs to buy, it wants to investigate if the mean lifetimes of the four types of light bulbs are the same. The company€™s research department randomly selected a few bulbs of each type and tested them. The following table lists the number of hours (in thousands) that each of the bulbs in each brand lasted before being burned out.

At a 2.5% significance level, test the null hypothesis that the mean lifetime of bulbs for each of these four brands is the same.

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Brand I Brand II Brand III Brand IV 26 24 21 29 28 24 28 19 24 19 26 27 25 26 18 20 21 27 19