Final answer:
The question appears to be a riddle and does not have enough context to provide an exact mathematical answer. The phrase '20th child of a London stockbroker' may be a hint towards a pattern or sequence, a historical figure, a financial term, or a cultural reference.
Step-by-step explanation:
The question "What is the 20th child of a London stockbroker?" seems to be a play on words and may not directly relate to a mathematics problem. However, if the question were intended to be a riddle or a play on numerical sequencing or pattern recognition, we could assume the 'child' refers to a term in a sequence. Without additional context or information about a sequence or pattern, it's not possible to provide an exact answer. If this is part of a riddle or joke, context is necessary to provide an appropriate response. In puzzle or riddle scenarios, 'the 20th child of a London stockbroker' might be a playful hint at a historical figure, a term from finance, or a cultural reference.