This is a very old puzzle as can be seen by the use of farthings, and the cost of a meal at the time.
For those of you who are not familiar with pre-decimalisation money, and farthings in particular: there were twelve pennies in a shilling and four farthings in a penny.
So, onto the puzzle itself. A group visited a restaurant for a meal. Each person in the group ordered exactly the same meal, and thus the cost of each person's meal was identical. The total bill came to six shillings and one farthing.
How many people dined together in this group?
The first thing to do is calculate the number of farthings that the final bill represents. Six shillings is 72 pennies, and 72 pennies is 288 farthings. Plus the one farthing gives a total of 289 farthings.
The number of people that dined must be a factor of 289, and as it happens 289 is 17 squared.
The number of people in the dining party must be 17.
As an aside, each person's meal must have cost 17 farthings, or fourpence one farthing - about 2p in today's money.