Question

pH measurements of a chemical solutions have mean 6.5 with standard deviation 0.02. Assuming all pH measurements of this solution have a nearly symmetric/bell-curve distribution. Find the percent (%) of pH measurements reading below 6.46 OR above 6.48.

Answer 1

µ =    6.5                              
σ =    0.02                              
  
P (   6.46   < X <   6.48   )                  
=P( (6.46-6.5)/0.02 < (X-µ)/σ < (6.48-6.5)/0.02 )                                  
                                  
P (    -2.000   < Z <    -1.000   )                   
= P ( Z <    -1.000   ) - P ( Z <   -2.00   ) =    0.1587   -    0.0228   =    0.1359

required percentage = 1-0.1359 = 0.8641 or 86.41%