6.16 Breaking bolts. Mechanical measurements on suppos edly identical objects usually vary. The variation often follows a Normal distribution. The stress required to break a type of bolt varies Normally with mean 75 kilopounds per square inch

(ksi) and standard deviation 8.3 ksi.

(a) What percent of these bolts will withstand a stress of 90 ksi without breaking?

(b) What range covers the middle 50% of breaking strengths for these bolts?

Soap in the shower. From Rex Boggs in Australia comes an un usual data set: before showering in the morning, he weighed the bar of soap in his shower stall. The weight goes down as the soap is used.

The data appear below (weights in grams). Notice that Mr. Boggs forgot to weigh the soap on some days. Exercises 6.17 to 6.19 are based on the soap data set.

Day Weight Day Weight Day Weight 92769 1 124 8 84 16 27 121 9 78 18 16 5. 103 10 71 19 12 96 12 58 20 8 90 13 50 21 6