Brothers and sisters

Lenka has as many brothers as sisters. Her brothers have twice as many sisters as brothers. How many brothers and sisters are in the family?

Correct answer:

b =  3
s =  4

Step-by-step explanation:

$$\begin{gathered} b=s-1 \\ 2(b-1)=s \\ 2(b-1)=b+1 \\ 2\cdot (b-1)=b+1 \\ b=3 \\ b=\frac{3}{1}=3 \\ b=3 \end{gathered}$$

Try another example