"Maffematiks" and "Rithmetik" were never my strong points - see my Tag Line - but armed with paper and pencil, I'll submit a "Revised Guestimate"
400 thingumies = 40 post TPD bottles.
On a temperate week I'll use 2 bottles a week; on a week where I have to wrestle with Call Centres, Wrangle Numpties etc it'll be 3 bottles.
So checked by the Incredble Human Computer, my wife, the answer is either 20 weeks or 13 and a bit weeks.
400 thingumies = 40 post TPD bottles.
On a temperate week I'll use 2 bottles a week; on a week where I have to wrestle with Call Centres, Wrangle Numpties etc it'll be 3 bottles.
So checked by the Incredble Human Computer, my wife, the answer is either 20 weeks or 13 and a bit weeks.