The ratio of the number of boys and the number of girl in a class is 9:11. If the number of boys is 18, then the number of girls is ____.

Answer

To solve the problem, we need to find the number of girls in a class given the ratio of boys to girls and the number of boys.

### Step-by-Step Solution:

1. **Understand the Ratio**: The ratio of boys to girls is given as 9:11. This means that for every 9 boys, there are 11 girls.

2. **Identify the Number of Boys**: We are told that the number of boys is 18.

3. **Set Up the Ratio**: We can express the number of boys and girls in terms of the ratio:
- Let the number of boys = 9x
- Let the number of girls = 11x
Here, x is a common multiplier.

4. **Find the Value of x**: Since we know that the number of boys is 18, we can set up the equation:
\[ 9x = 18 \]
To find x, divide both sides by 9:
\[ x = \frac{18}{9} = 2 \]

5. **Calculate the Number of Girls**: Now that we have the value of x, we can find the number of girls:
\[ \text{Number of girls} = 11x = 11 \times 2 = 22 \]

6. **Final Answer**: Therefore, the number of girls in the class is 22.

### Summary:
The number of girls in the class is **22**.