Question

Consider the following sample of observations on coating thickness for low-viscosity paint.

Assume that the distribution of coating thickness is normal (a normal probability plot strongly supports this assumption).

(a) Calculate a point estimate of the mean value of coating thickness. (Round your answer to four decimal places.)

(b) Calculate a point estimate of the median of the coating thickness distribution. (Round your answer to four decimal places.)

Answer 1

1)

c)

for 90th percentile , critical value of z =1.28

therefore value that separates the largest 10% from the remaining 90% =mean+z*standard deviation =1.7763

d_)

P(X<1.5)=P(Z<(1.5-1.3581)/0.3267)=P(Z<0.43)=0.6664

e)

estimated standard error =s/√n =0.0817

2)
b)

separates the weakest 50% of all such beams from the strongest 50% =median=7.7