Kevlar epoxy is a material used on the NASA space shuttles. Strands of this epox

Question

Kevlar epoxy is a material used on the NASA space shuttles. Strands of this epoxy were tested at the 90% breaking strength. The following data represent time to failure (in hours) for a random sample of 50 epoxy strands. Let x be a random variable representing time to failure (in hours) at 90% breaking strength. 0.54 1.80 1.52 2.05 1.03 1.18 0.80 1.33 1.29 1.13 3.34 1.54 0.08 0.12 0.60 0.72 0.92 1.05 1.43 3.02 1.81 2.17 0.63 0.56 0.03 0.09 0.18 0.34 1.51 1.45 1.52 0.19 1.55 0.01 0.07 0.65 0.40 0.24 1.51 1.45 1.60 1.80 4.69 0.08 7.89 1.58 1.62 0.03 0.23 0.72

(a) Find the range.

(b) Use a calculator to calculate x and x2. (Round your answers to two decimal places.) x = x2 =

(c) Use the results of part (b) to compute the sample mean, variance, and standard deviation for the time to failure. (Round your answers to two decimal places.) x = s2 = s =

(d) Use the results of part (c) to compute the coefficient of variation. (Round your answer to the nearest whole number.) %

Explanation / Answer

(a) Range = maximum value - minimum value = 7.89 - 0.01 = 7.88

(b) sum(x) = 62.09 and sum(x^2) = 164.15

(c) mean(x) = sum(x)/(no of observations) = 62.09 / 50 = 1.24 and

var(x) = 1/50 * sum(x^2) -mean(x) ^2 = 164.15 / 50 - 1.24^2 = 1.74

(d) cv = standard deviation / mean *100 % = sq.root(1.74) / 1.24 * 100 = 106.38

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