Huh? There's never been a 50/50 sale. They've been 90/10 in the past.
19. New Year's Step-Up (12/30/16 - 1/6/17): Three 11-roll steps, step 1 ($100): regular rates, step 2 ($50): 5* and 6* only (95%/5%), step 3 ($30): 5* and 6* only (90%/10%)
29. Spring Break Cleaning Gacha (3/2 - 3/9): Three 11-roll steps, $70/$50/$30, first step contains 4*-6* (82%/16.5%/1.5%), step 2 contains 5*-6* (95%/5%), step 3 contains 5*-6* (90%/10%)