Solving only Q1, As this questions has 2 questions only one can be answered in a single solution.

Mean = u = 1100

Std dev = Sigma = 60

z= (x-u)/(sigma)

(a) z = (1200-1100)/60 = 100/60 = 1.67

From Z table looking at the probability corresponding to 1.67 is 0.9525.

This means that 1-0.9525 = 0.0475 or 4.75% will survive more than 1200

b) z = (995-1100)/60 = -105/60 = -1.75

From Z table looking at the probability corresponding to -1.75 is 0.0401 or 4.01%

d) Probability is 10% or 0.1 Looking from Z table we get z= – 1.28 = (x- 1100)/60 => x= 1023.2

Warranty should be 1023 hrs.

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