SOLUTION: There is a bag with 5 red marbles, 11 blue marbles and 4 green marbles. If you always draw tokens without replacement, what is the probability that you: a. need to draw more th

Question 1166422: There is a bag with 5 red marbles, 11 blue marbles and 4 green marbles. If you always draw tokens without replacement, what is the probability that you:
a. need to draw more than 4 marbles to get a red marble
b. draw 4 marbles and get only one green marble
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
find probability draw fewer than 4 marbles to get a red one
for the first one red is 5/20=0.25
for the second one red is (15/20)(5/19)=0.1974
for the third one red is (15/20)(14/19)(5/18)=0.1535
for the fourth one red is (15/20)(14/19)(13/18)(5/17)=0.1174
That sum is 0.7883
Therefore, the probability it will require more than 4 draws is the complement or 0.2117
Draw 4 and get only 1 green
on the first (4/20) or 0.2
on the second (16/20)(4/19)=0.1684
on the third (16/20)(15/19(4/18)=0.1404
on the fourth (16/20)(15/19)(14/18)(4/17)=0.1156
That sum is the answer or 0.6244

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