Probability of an event happening=(numbers of ways it can happen) / (total numbers of outcomes)
P=probability that we are both selected
P₁=probability that I am selected and my brother is selected after.
P₂=probability that my brother is selected and I am selected afer.
P=P₁+P₂
P₁=(1/100)*(1/99)=1/9900
P₂=(1/100)*(1/99)=1/9900
P=1/9900 + 1/9900=2/9900≈0,0002≈0.02%
solution: P=2/9900≈0.02%