The variables
![a,b,c,d,](/media/m/3/4/f/34f869216efcc43c10d741b61522e803.png)
traverse, independently from each other, the set of positive real values. What are the values which the expression
![S= \frac{a}{a+b+d} + \frac{b}{a+b+c} + \frac{c}{b+c+d} + \frac{d}{a+c+d}](/media/m/5/3/a/53af05cd31ca682d7c3c6ffc742c0a41.png)
takes?
%V0
The variables $a,b,c,d,$ traverse, independently from each other, the set of positive real values. What are the values which the expression $$S= \frac{a}{a+b+d} + \frac{b}{a+b+c} + \frac{c}{b+c+d} + \frac{d}{a+c+d}$$ takes?