SOLUTION: If P(A or B) = 0.8, P(A)= 0.1 and P(B) = 0.9 determine P(A and B)

Question 424673: If P(A or B) = 0.8, P(A)= 0.1 and P(B) = 0.9 determine P(A and B)
Answer by linh117(31) (Show Source): You can put this solution on YOUR website!
P(A or B)= P(A) + P(B) - P(A and B)
0.8=0.1+0.9-x
Since x is on the right-hand side of the equation, switch the sides so it is on the left-hand side of the equation.
0.1+0.9-x=0.8
Add 0.9 to 0.1 to get 1.
1-x=0.8
Since 1 does not contain the variable to solve for, move it to the right-hand side of the equation by subtracting 1 from both sides.
-x=-1+0.8
Add 0.8 to -1 to get -0.2.
-x=-0.2
Multiply each term in the equation by -1.
-x*-1=-0.2*-1
Multiply -x by -1 to get x.
x=-0.2*-1
Multiply -0.2 by -1 to get 0.2.
x=0.2
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