In a school, there are $720$ students. If there are $300$ boys, then find the ratio of the number of girls to that of boys.

Check whether the following set of numbers are in proportion or not in the given order.

$2, 3, 2016, 2019$

Check whether the following set of numbers are in proportion or not in the given order.

$12, 15, 32, 40$

Find the value of $x$ in the following proportion.

$17:68::7:x$

Find the value of $x$ in the following proportion.

$14:42::x:27$

Arrange the following set of numbers in the order such that they should be in proportion. Hence, find the product of extremes.

$45, 9, 27, 15$

Arrange the following set of numbers in the order such that they should be in proportion. Hence, find the product of extremes.

$\frac{1}{6}, \frac{1}{15}, \frac{1}{40}, \frac{4}{9}$