1949+1950+1951+……+2010=(1949+2010)*62/2
1950+1951+1952+……+2010=(1950+2010)*61/2
(1949+2010)*62/2/(1950+2010)*61/2
=3959*62/3960*61
=122729/120780
1949+1950+1951+……+2010=(1949+2010)*62/2
1950+1951+1952+……+2010=(1950+2010)*61/2
(1949+2010)*62/2/(1950+2010)*61/2
=3959*62/3960*61
=122729/120780