Question 917486
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Hi
Trouble only because Totals hadn't been filled in:
Grade___Students__>8 HRS.__<8 HRS.
 A_______13_______12_______1
 B_______10_______8________2
 C_______8________6________2
 D_______9________2________7
 F_______10_______1________9
Tot______50______29________21 
P(A|B) = P(A and B)/P(B)
P(A |  &#8804; 8) =   {{{(1/50)/ (21/50)}}} = 1/21 = .05 rounded