3.2

Kevlar epoxy is a material used on the NASA space shuttles.Strands of this epoxy were tested at the 90% breaking strength. Thefollowing data represent time to failure (in hours) for a randomsample of 50 epoxy strands. Let x be a random variablerepresenting time to failure (in hours) at 90% breakingstrength.

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	0.02	0.07	0.65	0.40	0.24	1.51	1.45
1.60	1.80	4.69	0.08	7.89	1.58	1.63	0.03	0.23	0.72

(a) Find the range.


(b) Use a calculator to calculate ?x and?x². (Round your answers to two decimalplaces.)

?x	=
?x2	=

(c) Use the results of part (b) to compute the sample mean,variance, and standard deviation for the time to failure. (Roundyour answers to two decimal places.)

x	=
s2	=
s	=

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

What does this number say about time to failure?

The standard deviation of the time to failure is just slightlysmaller than the average time.The coefficient of variation saysnothing about time to failure.    The standarddeviation of the time to failure is just slightly larger than theaverage time.The standard deviation is equal to the average.

Why does a small CV indicate more consistent data, whereasa larger CV indicates less consistent data? Explain.

A small CV indicates more consistent data because thevalue of s in the numerator is smaller.A small CVindicates more consistent data because the value of s inthe numerator is larger.    

Consider sample data with

x = 8

and

s = 2.

(a) Compute the coefficient of variation.


(b) Compute a 75% Chebyshev interval around the sample mean.

Lower Limit
Upper Limit