So would a decent formula for drugs A and B be: rAdiff x rBdiff x rshared = r% where the rA/Bdiff is the chance of resisting the unique parts of A and B and rsh

So would a decent formula for drugs A and B be: rAdiff x rBdiff x rshared = r% where the rA/Bdiff is the chance of resisting the unique parts of A and B and rshared is the chance of resisting what is shared between them?