Two families A, B with equal numbers of children. 3 tickets distributed so no child gets more than one. If P(all to family B)=121, find the number of children in each family.
Solutions · 1
Official solution
With x children per family:
\[\frac{{}^xC_3}{{}^{2x}C_3}=\frac{1}{12} \implies \frac{x-2}{2(2x-1)}=\frac{1}{12} \implies x=5\]