Question 86637
Problem #1
Let A and B be independent events with P(A) = (1)/(4) and P(B) = (1)/(5) 
Find P (A (An upside down letter U) B)= (1/4)(1/5) = 1/20
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and P (A U B) = P(A) + P(B) - P(A and B)
= (1/4) + 1/5) -1/20
= 9/20-1/20
= 8/20
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Problem #2
In the previous section, we described an experiment in which the numbers 1, 2, 3, 4, and 5 are written on slips of paper, and 2 slips are drawn at random one at a time without replacement. Find each probability
Sample space: 
1+2=3; 1+3=4; 1+4=5 ;1+5=6
2+1=3;        2+3=5; 2+4=6 ; 2+5=7 
       3+1=4; 3+2=5;         3+4=7; 3+5= 8
              4+1=5; 4+2=6;  4+3=7;        4+5=9
                     5+1=6;  5+2=7; 5+3=8; 5+4=9
The probability that the first number is 3, given the following.
a. P(The sum is 7) = 1/20
b. P(The sum is 8) = 2/20
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Cheers,
Stan H..