Where to find it:

NodeGraph / Right Mouse Click / Add Nodes / Math / Extension Pack / D /

Returns A or B based on a Base Value and Probability e.g 

if Base >= Probability return A, else B

•A

Possible Output

•B

Possible Output

•Probability

Chance of A

•Base

Base Value to compare against Probability

•Output RGB

Separate computation for Input Channels Red, Green, Blue with an Alpha Channel of 1.0

•R

Computation for Input Red channel only, saved into R, G and B channel with an Alpha of 1.0

•G

Computation for Input Green channel only, saved into R, G and B channel with an Alpha of 1.0

•B

Computation for Input Blue channel only, saved into R, G and B channel with an Alpha of 1.0

•A

Computation for Input Alpha channel only, saved into R, G and B channel with an Alpha of 1.0