A company claims a mean bulb life of 42 months. A sample of 36 yields a mean of 39 months with a standard deviation of 7 months. Test the null hypothesis, Ho: mu >/=42 with alpha 0.05. Solution Zo = x -/(/n) =39-42/3 =-1.732 mod (Zo) =1.732 We calculate Z/2 Z0.025 =1.96 [=0.05] Since Z0.025 > mod (Zo) So Ho is accepted . Thus >=42.