Megan C. answered 10/31/19
Tulane/Yale Grad Experienced in Tutoring Math, Statistics, Test Prep
You are interested in the probability that the red shirt gets picked on the first or second try:
P(first try) = 10/18 [10 red/18 total shirts]
PLUS
P(second) = (8/18)*(10/17) [(8 non red/18 total)*(10 red/17 total remaining)]
This is equal to 1 minus the probability that a red shirt is never selected
P(never) = (8/18)*(7/17)