Express the following ratio in their simplest form.

$16:20$

Express the following ratio in the simplest form.

$5:6$

Express the following ratio in the simplest form.

$20:60$

Express the following ratio in the simplest form.

$8:15$

Express the following ratio in the simplest form.

$19:2$

There are $32$ students in a class of which $12$ are girls. Find the ratio of the number of boys to the total number of students

There are $32$ students in a class of which $12$ are girls. Find the ratio of the number of girls to the total number of students.