$1$

$\frac{p(1-q)(1-r) + q(1-p)(1-r) + r(1-p)(1-q)}{p(1-q)(1-r) + q(1-p)(1-r) + r(1-p)(1-q)}$

$\frac{pqr}{p+q+r}$

$p+q+r$