B3. In a class, there are 23 students, each of whom has chosen exactly one foreign language, either German or French. There are a total of 10 girls in the class, and there are 11 students in total who are taking French. The number of girls who have chosen French plus the number of boys who have chosen German is 16.

How many girls have chosen French?
B3. 7 In total, there are 23 students. From the data it follows:

$$
\begin{aligned}
16+11+10= & (\text { girls with French }+ \text { boys with German })+\text { everyone with French }+ \text { all girls } \\
= & (\text { girls with French }+ \text { boys with German }) \\
& +(\text { girls with French }+ \text { boys with French }) \\
& +(\text { girls with French }+ \text { girls with German }) \\
= & 3 \times \text { girls with French }+ \text { boys with German } \\
& + \text { boys with French }+ \text { girls with German } \\
= & 2 \times \text { girls with French }+23 .
\end{aligned}
$$

The number of girls with French is thus equal to $\frac{16+11+10-23}{2}=\frac{14}{2}=7$.