! The accompanying data in the table below were derived from life tests for two different brands of cutting tools. Complete parts a through . | | BR Click the icon 1o view the data table of cutting speed and useful life. E Click the icon to view the table of critical values of t. | ' I a. Use a 90% confidence interval to estimate the mean useful life of a brand A cutting tool when the cutti ng speed Is 45 meters per minute. Repeat for brand B. Compare the widths of the two intervals and comment on the reasons for any difference. The mean useful life of a brand A cutting tool when the cutting speed is 45 meters per minute is 2.7 to 3.9 hours. (Round to one decimal place as needed.) The mean useful life of a brand B cutting tool when the cutting speed is 45 meters per minute is D to D hours. (Round to one decimal place as needed.) Data table '- o | Cutting Speed Useful Life (Hours) | e Brand A Brand B \" 30 22 62 ' 30 37 6.1 | 30 54 46 ' 40 47 6.0 40 3.8 4.1 40 25 50 50 44 45 50 - 28 40 50 1.0 37 - 60 40 38 60 20 30 60 1.1 24 70 : 1.4 15 ' 70 05 2.0 70 30 1.0