Question

Weaver (1990) examined a galvanized coating process for large pipes. Standards call for an average coating weight of 200 lbs per pipe. Coating weights for 30 random pipes are given here lbs).

216 202 208 208 212 202 193 208 206 206

206 213 204 204 204 218 204 198 207 218

204 212 212 205 203 196 216 200 215 202

(c) (2 points) Construct and interpret a 95% rejection interval.

(e) (2 points) How comfortable are you with the assumptions needed for these analyses? Why?

Answer 1

(c)

H0: Null Hypothesis: = 200

HA: Alternative Hypothesis: 200

= 0.05

ndf = 30 - 1 = 29

From Table, critical values of t = 2.0452

Rejection Region:

Reject null hypothesis if

t_STST < - 2.0452

OR

t_STAT > 2.0452

(e) We are not comfortable with the assumptions needed or theseanalysis.

REASON:

The population SD is not provided and it is to estimated from sample SD. For applying t distribution, the population must be distributed as Normal Distribution. But, in the details provided, it is not written that the population is normally distributed.