A         B

         N      120      130

    mean      32 y     33.2 y

        SD     7.2 y     7.5 y

     t_calc  =      _{meanA - meanB}                               33.2 - 32.0

                             ----------------------------                      --------------------------------

                           [Standard error of the difference           √(51.84/120)+(56.25/130)

                              between two means]

                  _{=       1.2 /  0.9299          =       1.2905}  

       t_{(0.05)(248 df)  =     1.96     (note that any df >120 is read on the bottom line of each column as the "infinity" value.  In the case of alpha level 0.05, that value is 1.96 and does not change any further with increasing df size)}

_{The calculated t does not meet the critical t needed for significance, and therefore we are unable to reject the null hypothesis.   There is a difference in ages between the two groups;  Group B is slightly older than A (mean = 1.2 years more) but this is probably (much more than 5% likely) caused by chance alone.}       

  _{meanB - meanA   =   1.2,     248 df,     t= 1.2906     P>0.05   n.s.}