For n trials the binomial terms are:
2/2=0.10^2=0.01
1/2=2*0.10*0.90=0.18
0/2=0.90^2=0.81
These probabilities sum to 1. 0.90 is the probability of failure when 0.10 is the probability of success.
The table shows the probability of X out of 2 trials, denoted by X/2.
From this table the probability of 1/2 is 0.18.