How many girls are 16?

Question

There are 450 students in the 10th grade. Of these, 46% are boys, and 21% are girls who have already turned 16. How many girls in 10th grade are 16? 

Answer 1

450 is the total amount of students in the 10th grade. 21% is the amount of girls that are 16 years old. We can express two fractions from this information and equate them to one another.

 

21% is just 21 out of 100, so that's our first fraction.

 

21/100

 

We want to know how many x students out of the total 450 students are represented by that percentage. There's our second fraction.

 

x/450

 

 

Now we equate the two fractions and solve for the variable x.

 

21/100 = x/450

 

x = (21/100)*450 = (0.21)*450 = 94.5 ≈ 95

 

So 95 girls in the 10th grade are 16. We round up to the nearest whole girl.

 

There's no need to worry about the percentage of boys because we're only concerned with the 16-year old girls. It seems the information about the boys is meant to distract us. Also, notice that 46% plus 21% doesn't add up to 100%. The missing 33% are girls who are not yet 16. That information isn't necessary either, but it's there just in case you were curious.