Question 1069795
prob A+=1/2
prob B+=2/3
assuming independence, for both it is (1/2)(2/3)=(1/3)
for only 1 it is 1-both-0.  For both it is 1/3; for neither it is (1/2)(1/3)=(1/6)  That sum is 1/2 and 1-1/2=1/2.
Or, the (1/6) for A but not B and (1/3) for B but not A, and that sums to 1/2.
Neither hits is (1/6) as shown above.