In a group of 6 males and 4 females, four persons are to be selected such that
at least one boy should be there.
So we can have
(four males) or (three males and one female) or (two males and two females) or (one male and three females)
This combination question can be solved as
(6C4)+(6C3** 4C1)+(6C2** 4C2)+(6C1**4C3)=[15 + (20*4)+(15*6)+(6*4)]=15+80+90+24=209