解析见内

This is how many total ways:

C(10,2)*C(8,2)*C(6,2)*C(4,2)*C(2,2)/2^5

This is the probability each pair matches:

(1*1/9)*(1*1/7)*(1*1/5)*(1*1/3)*(1*1/1)

Time these two together is the answer