Why does Jim's mother take so long to count the money?

From the text:

It was a long, difficult business, for the coins were of all countries and sizes--doubloons, and louis d'ors, and guineas, and pieces of eight, and I know not what besides, all shaken together at random. The guineas, too, were about the scarcest, and it was with these only that my mother knew how to make her count.

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