You never learned the easy way to do LSD? It was quite simple. Say you have three items, one and tenpence-ha'penny, two- and-eleven, and 5/9. Round up- two bob, 3 bob, 6 bob. That's eleven shillings. Now take off the odd bits, penny-ha'penny, penny and threepence. That's fivepence ha'penny, Knock that off the eleven bob, and you've got ten-and-sixpence-ha'penny.

Now calculate 5lb of carrots at eightpence ha'penny a pound, 18lb of potatoes at 1/9 a stone, 3 ounces of bacon at 2/7 a pound, and a quart of vinegar at 19/4 a gallon...