Larry graduated this year and finally has a job. He's making a lot of money, but somehow never seems to have enough. Larry has decided that he needs to grab hold of his financial portfolio and solve his financing problems. The
first step is to figure out what's been going on with his money. Larry has his bank account statements and wants to see how much money he has. Help Larry by writing a program to take his closing balance from each of the past twelve months and calculate his
average account balance.

The input will be twelve lines. Each line will contain the closing balance of his bank account for a particular month. Each number will be positive and displayed to the penny. No dollar sign will be included.

The output will be a single number, the average (mean) of the closing balances for the twelve months. It will be rounded to the nearest penny, preceded immediately by a dollar sign, and followed by the end-of-line. There will be
no other spaces or characters in the output.

这个问题实在太简单，要说有什么难的就是小弟的英语水平跟不上打字水平。由于实在太简单，我就不按老规矩分析了，只是指出需要注意的方面并拓展。

• 听江湖传言，WA最多的就是精度问题了。不少同志由于不是用Java，所以精度没控制好。

对于这个问题，下面列出四种java里面的解决方法：

1. 最简单的，System.out.println(String.format("%.2f", f));或者System.out,printf("%.2f",a);
2. DecimalFormat df = new DecimalFormat("#.00");  System.out.println(df.format(f));
3. 1. NumberFormat nf = NumberFormat.getNumberInstance();
   2. nf.setMaximumFractionDigits(2);
   3. System.out.println(nf.format(f));
4. 1. BigDecimal bg = new BigDecimal(f);
   2. double f1 = bg.setScale(2, BigDecimal.ROUND_HALF_UP).doubleValue();
   3. System.out.println(f1);

感谢总结上面方法的同志！

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