Genetic counsellors can identify heterozygous individuals by

The number of ways of arranging $8$ men and $4$ women around a circular table such that no two women can sit together is

The harmonic mean of $\frac{a}{1 - ab}$ and $\frac{a}{1 + ab}$ is

$A$ ball is dropped from a height $h$ on a floor of coefficient of restitution $e$. The total distance covered by the ball just before the second hit is

An achromatic combination of lenses produces