Cindy has 400 x 2 = <<400*2=800>>800 cards.
Nicole and Cindy have 400 + 800 = <<400+800=1200>>1200 cards.
Rex has 1200/2 = <<1200/2=600>>600 cards.
Rex is left with 600/(3+1=4) = <<600/4=150>>150 cards
#### 150