A fruit grower wants to test a new spray that a manufacturer claims will reduce the loss due to insect damage. To test the claim, the grower sprays 200 trees with the new spray and 200 other trees with the standard spray. The following data were recorded:

a. Do the data provide sufficient evidence to conclude that the mean yield per tree treated with the new spray exceeds that for trees treated with the standard spray? Use α = .05.
b. Construct a 95% confidence interval for the difference between the mean yields for the two sprays.

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New Spray Mean Yield per Tree x (lb) 240 Variances Standard Spray 227 820 980