P9(1)=C(9;1)*0,5^1*0,5^8=9/512
P9(2)=C(9;2)*0,5^2*0,5^7=36/512
P9(3)=C(9;3)*0,5^3*0,5^6=84/512
P(A)=9/512+36/512+84/512=129/512=0,2519531≈0,25
получилось так