Why is a pony twentyfive pounds?

Answer 1

According to businessballs.com the expression ponyis explained in the following manner:

pony - twenty-five pounds (£25). From the late 18th century according to most sources, London slang, but the precise origin is not known. Also expressed in cockney rhyming slang as 'macaroni'. It is suggested by some that the pony slang for £25 derives from the typical price paid for a small horse, but in those times £25 would have been an unusually high price for a pony. Others have suggested that an Indian twenty-five rupee banknote featured a pony. Another suggestion (Ack P Bessell) is that pony might derive from the Latin words 'legem pone', which (according to the etymology source emtymonline.com) means, "........ 'payment of money, cash down,' [which interpretation apparently first appeared in] 1573, from first two words [and also the subtitle] of the fifth division of Psalm cxix [Psalm 119, verses 33 to 48, from The Bible's Old Testament], which begins the psalms at Matins on the 25th of the month; consequently associated with March 25, a quarter day in the old financial calendar, when payments and debts came due...." The words 'Legem pone' do not translate literally into monetary meaning, in the Psalm they words actually seem to equate to 'Teach me..' which is the corresponding phrase in the King James edition of the Bible. Other suggestions connecting the word pony with money include the Old German word 'poniren' meaning to pay, and a strange expression from the early 1800s, "There's no touching her, even for a poney [sic]," which apparently referred to a widow, Mrs Robinson, both of which appear in a collection of 'answers to correspondents' sent by readers and published by the Daily Mail in the 1990s.

Answer 2

The weight of a pony can vary depending on breed, size, and age. Generally, ponies can weigh between 400 to 900 pounds, with some pony breeds such as the Shetland pony weighing on the lower end of that range. It seems unlikely for a pony to weigh only twenty-five pounds, as that would be abnormally light and likely unhealthy for the animal.