Can you explain the rhymes here? I can't figure them out.
20: score. a very old word for 20. e.g. "threescore years and ten" is from the bible.
25: pony. no one knows for sure. some say it's because an indian 25 rupee note had a pony on it, but I've never seen anyone back that up with a picture or even any evidence that this note existed.
100: ton. tonnage is the measure of capacity of a ship (so volume not weight). 100 cubic feet are in one maritime ton.
500: monkey. again no one knows. again said to be from a 500 rupee note but no one has an image of one.
1000: grand. actually from american slang of around 1915. $1000 was "a grand sum".