IQuestion about XSLT and Math Operations

Hi,
i would like to know if i can perform some math operation between fields
generated by xslt without use variables

Example:
XML`

<?xml version="1.0"?>
<test>
     <parameters>
          <r2>200000</r2>
          <r3>1</r3>
          <r31>1</r31>
     </parameters>
<test>


XSLT`


<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
     <xsl:output method="xml" omit-xml-declaration="yes" indent="yes"/>
     <xsl:template match="parameters">
          <xsl:param name="r50">
                <xsl:value-of select="r3*r2"/>
          </xsl:param>
          <elab>
                <tab0>
                     <r10>
                          <c0>null</c0>
                          <c1>
                               <xsl:value-of select="r2"/>
                          </c1>
                          <c2><xsl:value-of select="$r50"/></c2>
                     </r10>
                     <r11>
                          <c0>
                               <xsl:value-of select="r2"/>
                          </c0>
                          <c1>
                               <xsl:value-of select="r2 - r6"/>
                          </c1>
                          <c2>null</c2>
                     </r11>
                     <r12>
                          <c0>null</c0>
                          <c1>
                               <xsl:value-of select="r2 - r6"/>
                          </c1>
                          <c2>
                          How I can perform, if possible , this type of
operation: [value of r11/c1 + value of r12/c1] whithout use xsl:param.
</c2>
                     </r12>
                </tab0>
          </elab>
     </xsl:template>
</xsl:stylesheet>



Thank you very much

Hi