I am using version 1.3.9h and current theme 'Avignon'.

I have setup a radio button with 4 selection options; 10; 20; 50 & 100.

Each select option I have added, using Attributes Controller, the price attribute.

What I would like to do is;

using the radio button selection, lets say 20, I would like to use this figure and multiply that be qty required and then deduct that from the qty available.

For example I what 20 pack and I want qty of 3 that equals 60. Now the qty available is 150 so after the above has been done the resultant available will then be 90.