?$=\frac {1}{2}+(\frac {1}{3}+\frac {2}{3})+(\frac {1}{4}+\frac {2}{4}+\frac {3}{4})+(\frac {1}{5}+\frac {2}{5}+\frac {3}{5}+\frac {4}{5})$?
?$+.….+(\frac {1}{12}+\frac {2}{12}+.….+\frac {11}{12})$?
?$=\frac {1}{2}+\frac {2}{2}+\frac {3}{2}+\frac {4}{2}+.….+\frac {11}{2}$?
?$=\frac {1}{2}+1+\frac {3}{2}+2+.….+\frac {11}{2}$?
?$=15+\frac {36}{2}$?
?$=15+18$?
?$=33$?
