Brain Teaser – July 9

Answer: There are 7 children. Let S be the number of sons and D be the number of daughters. Then, since Jim has the same number of brothers and sisters, S-1 = D.

From the fact that Elena has twice as many brothers as she has sisters, we have 2x(D-1)=S. Therefore, S=2D-2.

If we substitute this in our first equation, we get 2D-2-1=D, so D=3, and, therefore, S =4. Hence, the total number of children is S+D=7.