Set percentage of assessment tasks completed to automatically update UoC to C

Set up for a unit of competency to have multiple assessment tasks mapped to it but the learner only needs to successfully complete a percentage of those assessment tasks to be found competent for that unit.  For example: 1 unit has 5 assessment tasks mapped but only requires the successful completion of 3.  I want the system to automatically update the UoC to competent once 3 are satisfactory.