In an agricultural experiment, the effects of two fertilizers on the production of oranges were measured. Sixteen randomly selected plots of land were treated with fertilizer A, and 12 randomly selected plots were treated with fertilizer B.

The number of pounds of harvested fruit was measured from each plot. Following are the results.

a. Explain why it is necessary to check whether the populations are approximately normal before constructing a confidence interval.

b. Following are boxplots of these data. Is it reasonable to assume that the populations are approximately normal?

c. If appropriate, construct a 98% confidence interval for the difference between the mean yields for the two types of fertilizer. If not appropriate, explain why not.

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Fertilizer A 445 523 464 483 441 491 403 466 448 457 437 516 417 420 400 506 Fertilizer B 362 414 408 398 382 368 393 437 387 373 424 384