Answer: The probability that the fourth marble Amy picks is black 
The probability that in the fifth attempt she will pick a red or a black marble P(R∩B) =
Step-by-step explanation:
To find the probability that in the fifth attempt she will pick a red or a black marble P(R∩B) .
The total marble in beginning=6+4+8=18
After 3 attempts, the total marbles left=18-3=15
The number of black marbles =8
The probability that the fourth marble Amy picks is black 
As four marble has already picked up, then the total marbles left in the box
=18-4=14
Now, as a red marble is already picked in 1st attempt , the number of red marbles in the box now= 4-1=3
And a black marble is already picked in fourth attempt , the number of black marbles in the box now= 8-1=7
Now P(R∩B)=P(R)+P(B)=
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Answer:
Step-by-step explanation: please go through the attached file for detailed explanation .