My son, recently returned from deployment, suffered (ha! - he'd return in a second) through a few days R&R while the ship visited Portsmouth.
Among the gifts he brought back was a set of pre-decimal coins, Shilling, Half-Crown, Florin, ha'penny, penny, farthing, threepence (2 sizes) and a sixpence.
I did spot in http://www.24carat.co.uk/denominations.html: "There were of course 20 shillings to the pound, twelve pence to the shilling, and therefore 240 pence to the pound."
so at least that's given me an idea.... and a farthing was a quarter-penny... a half crown ends up 2/6d, and a crown is 5/-
all obvious now ....