sum function

How do I use the sum function on xml such as:

<Amount>12,345.12</Amount>
<Amount>132,345.12</Amount>
<Amount>2,345.12</Amount>

If I use Total Price = <xsl:value-of select="sum(//Amount)"/> I get the
result NaN. However, if the data does not contain ',' the sum works
correctly.
Any help appreciated.
Regards
	Jan






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