# Question

A spring maker is supplying helical coil springs meeting the requirement for a spring rate k of 10 ± 1 lbf/in. The test program of the spring maker shows that the distribution of spring rate is well approximated by a normal distribution. The experience with inspection has shown that 8.1 percent are scrapped with k < 9 and 5.5 percent are scrapped with k > 11. Estimate the probability density function.

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