Question: why 12 pennies in a shilling?
Answer: 1 shilling equalled twelve pence (12d). There were 240 pennies to a pound because originally 240 silver penny coins weighed 1 pound (1lb). ... 10/- meaning ten shillings. An amount such as 12/6 would be pronounced 'twelve and six' as a more casual form of 'twelve shillings and sixpence'.