Assume that the helium porosity (in percentage) of coal samples taken from any particular seam is normally distributed with true standard deviation 0.79. (a) Compute a 95% CI for the true average porosity of a certain seam if the average porosity for 22 specimens from the seam was 4.85. (Round your answers to two decimal places.)

Answer:Interval=4.85±0.33Interval (5.18,4.52)Step-by-step explanation:Consider the formula for the interval:interval=[tex]X[/tex]±[tex]\frac{Z*S}{\sqrt{n} }[/tex]Where:X is the mean valueS is the standard deviationn is the sample sizeZ is the distributionAlpha=1-0.95=0.05[tex]Z_{alpha/2}=Z_{0.05/2} =Z_{0.025}[/tex]=1.96 (From Standard Z-Distribution Table)Now use the above formulainterval=[tex]4.85[/tex]±[tex]\frac{1.96*0.79}{\sqrt{22} }[/tex]Interval=4.85±0.33Interval (5.18,4.52)