only 2 combination helps us get the answer
we can solve it in 2 ways:
1)
a) we need x+y or x-y out of 4, then 2/4
b) then we need either of them, so 1/3
c)2/4*1/3=1/6
Or let's us combinatorics
there are totally 2C4 combinations of the 4 pairs, when 2 are chose. 2C4=6
there is only one combination that suits us, then 1/6
Answer is E
we can solve it in 2 ways:
1)
a) we need x+y or x-y out of 4, then 2/4
b) then we need either of them, so 1/3
c)2/4*1/3=1/6
Or let's us combinatorics
there are totally 2C4 combinations of the 4 pairs, when 2 are chose. 2C4=6
there is only one combination that suits us, then 1/6
Answer is E