I have a list of date ranges, let's say:

```
A B
1 April 25, 2013 May 31, 2013
2 September 30, 2013 October 18, 2013
```

I need to calculate a sum of net working days of all ranges into a single cell. I want to avoid intermediate =NETWORKDAYS(). An array formula is a logical choice, but an attempt to apply it, like this `{=SUM(NETWORKDAYS(A1:A2, B1:B2))}`

leads to a formula error.

How can it be done?

More broadly, how does Excel apply an array formula? It is not clear to me from basic array formula examples.