If a box contains twenty-one coloured discs, composed of fifteen blue discs and six red discs, and two discs were taken at random, it can be seen that the probability of taking two blue discs is.

• prob of selecting disc = 21 c 2
  prob of blue disc = 15
  p(blue disc) =15c2/21c2=1/2
• 11 years agoHelpfull: Yes(11) No(2)
• The first blue disk can be choose from 21 disks.
  So the probability is 15/21
  and the probability of taking 2nd blue disc is (15-1)/(21-1)
  So the probability of taking two blue discs is (15/21)*(14/20) = 1/2
• 11 years agoHelpfull: Yes(4) No(0)
• No. of ways two disc can be drawn:21C2=210
  No. of ways two blue discs can be drawn:15C2=105
  prob.=105/210=1/2
• 11 years agoHelpfull: Yes(4) No(0)
• n(s)=21c2
  n(E)=15c2
  P(E)=n(E)/n(s)=21c2/15c2 = 1/2
• 11 years agoHelpfull: Yes(3) No(2)