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Question Number 113605 by bobhans last updated on 14/Sep/20
A bag contains 6 red, 5 white and 4 black balls  If twl balls are drawn , what is the probability  that none of them are red ?
Abagcontains6red,5whiteand4blackballsIftwlballsaredrawn,whatistheprobabilitythatnoneofthemarered?
Commented by bemath last updated on 14/Sep/20
method_2  p(A)=(9/(15))×(8/(14)) =(3/5)×(4/7)=((12)/(35))
method_2p(A)=915×814=35×47=1235
Answered by bemath last updated on 14/Sep/20
method_1  n(S)= C_2 ^(15)  = ((15×14)/(2×1)) = 105  none of them are red→(2W),(2B),(1W,1B)  n(A)=C_2 ^5 +C_2 ^4 +C_1 ^5 ×C_1 ^4   n(A)= 10+6+20=36  so p(A) = ((36)/(105)) = ((12)/(35))
method_1n(S)=C215=15×142×1=105noneofthemarered(2W),(2B),(1W,1B)n(A)=C25+C24+C15×C14n(A)=10+6+20=36sop(A)=36105=1235

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