Why can I not get back a number from any of these methods

[wxdqz]

Why can I not get back a number from any of these methods adding the two variables defined here.

Since the first example returns values, I know my variables are not null.

<!--VARIBALE1 -->
<xsl:variable name="CountedSubTotal">
<xsl:value-of select="format-number(sum(SummaryReportSection1/Counted), '$##########0.00')"></xsl:value-of>
</xsl:variable>

<--!VARIABLE2 -->
<xsl:variable name="CountedTotal">
<xsl:value-of select="format-number(sum(SummaryReportSection2/Counted), '$##########0.00')"></xsl:value-of>
</xsl:variable>

<!--This returns the two numbers but as a string - example: $1689.19 + $859.37 -->
<xsl:copy-of select="$CountedTotal"/> + <xsl:copy-of select="$CountedSubTotal"/>

<!--All these other return NaN -->
<xsl:variable name="CountedTotalLine">
<xsl:value-of select="$CountedTotal + $CountedSubTotal"/>
</xsl:variable>
<xsl:copy-of select="$CountedTotalLine"/>


<xsl:value-of select="format-number($CountedTotal + $CountedSubTotal, '$##########0.00')" />


<xsl:variable name="CountedTotalLine" select="$CountedTotal + $CountedSubTotal"/>
<xsl:value-of select="$CountedTotal + $CountedSubTotal"></xsl:value-of>
<xsl:copy-of select="$CountedTotalLine"/> -->