In a class of 20, 12 are boys and 13 wear glasses. There are twice asmany boys with glasses as girls with no glasses. How many girls wearglasses?

Let's break down the problem:

1. We know that there are 20 students in total, 12 of which are boys. This means there are 20 - 12 = 8 girls in the class.

2. We also know that 13 students wear glasses.

3. The problem states that there are twice as many boys with glasses as there are girls without glasses.

Let's denote:

• The number of boys with glasses as B
• The number of girls without glasses as G

From the problem, we know that B = 2G.

4. Since there are 8 girls in total and some of them don't wear glasses (G), the number of girls who wear glasses is 8 - G.

5. The total number of students who wear glasses is the sum of boys with glasses and girls with glasses, which is B + (8 - G). But we know from the problem that this total is 13.

So we have the equation B + (8 - G) = 13.

6. Now we can substitute B = 2G from step 3 into this equation to get 2G + (8 - G) = 13.

7. Solving this equation gives G = 5. This means there are 5 girls who don't wear glasses.

8. Therefore, the number of girls who wear glasses is 8 - G = 8 - 5 = 3.

So, there are 3 girls who wear glasses in the class.