the example code for array.reduce can't get the expected result

the example code for `array.reduce` can't get the expected result.
in order to get the expected result 0, the second line  should change  `+`  to `-` .
```
[55, 44, 33, 22, 11].reduce(function(p, c, i, arr){
//return p + c/(arr. length-i);
return p - c/(arr. length-i);
}, 55); // 0
```
