Fred's classroom has a ratio of 2 girls:3 boys. how many students are in the class if there are 16 girls?

The ratio is 2:3

So you replace the 2 with 16 because that's the number of girls.

2:3 and be rewritten as 2/3

So 16:x (unknown number of boys can be written as 16/x. No you just solve for x so that both fractions are equivalent.

2 times 8 is 16, so that's the relationship between the numerator. Whatever you do to the top is done to the bottom, so 3 times 8 is 24.

Now you have the complete fraction: 16/24. This can be rewritten as the ratio: 16:24

Those are the numbers of boys and girls separately - now you just need to add them to get the total number of kids in the class.

16+24=40 students

Their are thirty people in the classroom.