on 29/08/2019, Tim+ supposed :
Now I know that in practice it doesnt matter a jot but every time I mix up
some two-stroke fuel I agonise (very slightly) over whether its one part
oil added to 50 parts petrol or one part oil *in* 50 parts petrol/oil mix
(hence one part oil added to 49 parts of petrol)

50 litres of fuel to 1 litre of oil, to make 51 litres in total.