On an airplane that was 2/3 full, 20% of the passengers were boys, one-fourth of the passengers were women, one-eighth of the passengers were girls, and there were 51 men. How many seats are on the plane
boys have $\displaystyle \frac{1}{5} seats$
women have $\displaystyle \frac {1}{4} seats$
girls have $\displaystyle \frac{1}{8} seats$
in all the total seats occupied by them
$\displaystyle
=\frac{1}{5}+ \frac {1}{4} + \frac{1}{8}
=\frac{23}{40}
$
so fraction of seats left $\displaystyle =1-\frac{23}{40}seats$
=51(that occupied by man)
so toal seats occupied by all
$\displaystyle
=\frac{40}{17}*51
=120
$
this is two third of total available
so total seats $\displaystyle = \frac{3}{2} *120=180$-----ANSWER