Students in a business statistics course performed a completely randomised design to test the strength of four brands of garbage bags. One hundred gram weights were placed into a bag one at a time until the bag broke. A total of 40 bags, 10 for each brand, was used. The data in the file

< GARBAGE_BAGS > give the weight (in kilograms) required to break the garbage bags.

a. At the 0.05 level of significance, is there evidence of a significant difference in the mean strength of the four brands of garbage bags?

b. If appropriate, determine which brands differ in mean strength.

c. At the 0.05 level of significance, is there evidence of a significant difference in the variation in strength between the four brands of garbage bags?

d. Which brand(s) should you buy and which brand(s) should you avoid? Explain.