His son, Jim, has the same number of brothers and sisters.
His daughter, Elena, has twice as many brothers as she has sisters.
How many children are in Dr. Johnson’s family?
See the answer
Answer: There are 7 children. Let S be the number of sons and D be the number of daughter. 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.