10.59 Light Bulbs A manufacturer of industrial light bulbs likes its bulbs to have a mean life that is acceptable to its customers and a variation in life that is relatively small. If some bulbs fail too early in their life, customers become annoyed and shift to competitive products. Large variations above the mean reduce replacement sales, and variation in general disrupts customers' replacement schedules. A sample of 20 bulbs tested produced the following lengths of life (in hours):

The manufacturer wishes to control the variability in length of life so that or is less than 150 hours. Do the data provide sufficient evidence to indicate that the manufacturer is achieving this goal? Test using a = 0.01.

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