I'M NOT 100% SURE THIS IS RIGHT, IT'SJUST HOW I'D WORK IT OUT
For [Boy, Girl, Boy] There are 10 boys, so theres a 1/10 chance he'll pick a boy, Then there are 12 girls, so 10×12=120 different lists so far. (because if he picks boy 1, and then there are 12 girls, if he picks boy 2 there are still 12 girls). for the last bit there are 9 boys left bc one of them have already been picked. so 120 x 9 = 1080. 1080 possibilities. For [Girl, Boy Girl] its a similar process but aince there are 12 girls it would be 12x10= 120. then 11 girls left so 120x11