A little boy bustled（喧闹，忙乱） into a grocery one day with a memorandum（便笺） in his hand.″Hello, Mr. Smith,″He said, ″I want thirteen pounds of coffee at 33 cents.″″Very good,″ said the grocer, and he noted down the sale.″Anything else, Charlie?″″Yes. Twenty－seven pounds of sugar at 9 cents.″″The loaf? And whatelse?″″Seven and a half pounds of bacon at 30 cents.″″That will be a good brand. Goon.″″Five pounds of tea at 90 cents, eleven and a half quarts of molasses at 8 cents a pint, two eight－pound hams at 31 cents, and five dozen jars of pickled walnuts（核桃） at 34 cents a jar.″The grocer made out the bill.″It's a big order,″ he said. ″Did your mother tell you to pay for it？″″My mother,″ said the boy, as he pocketed the neat and accurate bill, ″has nothing to do with this business. It is my arithmetic（算术） lesson and I had to get it done somehow.″