I don't know if I'm right but without accuracy (normal flinch rate=30%), I would say:
1 Rock Slide without Serene Grace: 49% no flinch, 9% two flinches, 42% one flinch
2 Rock Slides without Serene Grace: 24,01% no flinch, 26,01% two flinches, 49,98% one flinch
1 Rock Slide with Serene Grace...