sorry last time i was not clear about my qustion

is the following valid
i am trying to get  (third of the value of x )and (two third of the value
held in y )
such :1/3(x)+2/3(y)


<xsl:value-of select="(1 div 3 * (self::x)) + (2 div 3  * (self::y))"/>

thanks