It is important that face masks used by firefighters be able to withstand high t

Question

It is important that face masks used by firefighters be able to withstand high temperatures because firefighters commonly work in temperatures of 200- 500 degree F. In a test of one type of mask, 11 of 55 masks had lenses pop out at 250 degree. Construct a 90% upper confidence limit for the true proportion of masks of this type whose lenses would pop out at 250 degree. (Round your answers to four decimal places.) You may need to use the appropriate table in the Appendix of Tables to answer this question.

Explanation / Answer

Confidence Interval:

P^ = 11 / 55

     = 0.2

p^ (-/+) E

E = zc * sqrt ((p^*(1-p^))/n)

zc is the critical value at 10% level of significance from normal table as 1.645

E = 1.645 * sqrt ((0.2*(1-0.2))/55)

    = 0.0887

P^ (-/+) E

0.2 (-/+) 0.0887

0.1113 and 0.2887

Answer: 0.1113 and 0.2887

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