In a class of students, the ratio of boys to girls is 2: 3.if the number of boys is 30. 1.the number of girls. 2.the total number of students in the class

So let's make a ratio proportional to this
boys to girls
2/3  <--- the ratio
30/x  < we need to solve this
let's write as an equation and solve for the amount of girls
2/3 = 30/x
cross multiply
2x = 90
divide both sides by 2
x = 45

The number of girls is 45.
The total number of students in the class is 30 + 45 which is 75.

Hope this helps :)