(related to Problem: Awkward Money)
As a ching-chang is worth twopence and four-fifteenths of a ching-chang, the remaining eleven-fifteenths of a ching-chang must be worth twopence. Therefore eleven ching-changs are worth exactly thirty pence, or half a crown. Now, the exchange must be made with seven round-holed coins and one square-holed coin. Thus it will be seen that $7$ round-holed coins are worth seven-elevenths of $15$ ching-changs, and $1$ square-holed coin is worth one-eleventh of $16$ ching-changs — that is, $77$ rounds equal $105$ ching-changs and $11$ squares equal $16$ ching-changs. Therefore $77$ rounds added to $11$ squares equal $121$ ching-changs; or $7$ rounds and $1$ square equal $11$ ching-changs, or its equivalent, half a crown. This is more simple in practice than it looks here.
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