M is a girl and has the same number of brothers as sisters. N is a boy and has twice as many sisters as brothers. M and N are the children of Q. How many children does Q have?

Question: M is a girl and has the same number of brothers as sisters. N is a boy and has twice as many sisters as brothers. M and N are the children of Q. How many children does Q have?

Solution:
Let d and s represent the number of daughters and sons respectively.
Then, we have :
d - 1 = s
and
2(s - 1) = d
2s - 2 = s + 1
2s - s = 1 + 2
s = 3

d = 3 + 1 = 4

Total children = 4 + 3 = 7