Question 260308
Let X = bob and Y = kate
according to kate,
X: B = 2S
according to bob
Y: S = B
Now
kate + brothers + sisters = bob + brothers + 2*sisters
which means that
X + B + 2S = Y + B + S
subtracting B, we get
X + 2S = Y + S
subtracting S, we get
X + S= Y 
in other words,
kate = (multiple)*(brother + sister)
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So we have
bob has 2 brother and 4 sisters for a total of 7 kids
kate has 3 brothers and 3 sisters for a total of 7 kids
There are 3 boys and 4 girls