{(C10 2)/(C50 2)+(C18 2)/(C30 2)}/{(C10 1)/(C50 1)+(C18 1)/(C30 1)}={90/(50*49)+18*17/(30*29)}/{1/5+3/5}=(9/49*5+51/29*5)/(4/5)=(9*29+51*49)/(19*29*5)/(4/5)=2760/(19*29*4)=690/(19*29)=690/1421
