Question 226264
I think you got the right idea
:
Each girl in the Smith family has the same number of brothers as she has sisters.
For this to be true: g = b+1 (sisters 1 less than no. of girls)
:
 Each boy in the Smith family has twice as many sisters as he has brothers.
For this to be true: 2(b-1) = g (brothers a 1 less than no. of boys)
:
 How many girls and boys are there in the Smith family?
Replace g with b+1 in equation: 2(b-1) = g
2(b - 1) = b + 1
2b - 2 = b + 1
2b - b = 1 + 2
b = 3 boys
then using the 1st statement:
g = 3 + 1 = 4 girls
:
: 
see if that is true: 
girl has 3 brothers and 3 sisters (1st statement)
boy has 4 sisters, 2 brothers (2nd statement)