I have another opinion on the third question. Wonder, if it is right?
1) I got 1/30 too
2) got 1/6 as well
But, in my opinion, the third question should be solved this way:
the question asks what is the probability of AT LEAST one girl will be selected.
we have three mutually exclusive possibilities to select (they are all satisfy the asked condition):
GBB (girl,boy,boy)
GGB (girl,girl,boy)
GGG (girl,girl,girl)
the probability of GGG is already known - 1/30.
the probability of GGB is: 4/10*3/9*6/8 - 1/10.
the probability of GBB is: 4/10*6/9*5/8 - 1/6.
As these are mutually exclusive, we shall add them together: 1/30+1/10+1/6 = 3/10.
What do you think of this?
ANS.......
u r right but only mistake u r doing is that u have to multiply two of possiblities by 3....reason:-
possiblities of taking two girls is GGB,GBG,BGG ie 1/10*3=3/10.....
possiblities of taking two girls is GBB,BGB,BBG ie 1/6*3=1/2....
As these are mutually exclusive, we shall add them together: 1/30+3/10+1/2 = 5/6.
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