Fie x numarul spectatorilor din sala.Clasa I -> 1/5*x=x/5;
Clasa aII-a -> (x-x/5)*3/8=4x/5*3/8=12x/40=3x/10;
Clasa aIII-a -> [x-(x/5+3x/10)]*1/2=(x-5x/10)*1/2=(x-x/2)*1/2=x/4;
Clasa aIV-a -> x-(x/5+3x/10+x/4)=x-(8x+12x+10x)/40=x-30x/40;
Cum ultimul rest este reprezentat chiar de numarul de elevi de clasa a4-a, avem:
(x-30x/40)*2/5=16
(40x-30x)/40*2/5=16
10x/40*2/5=16
x/2*1/5=16
x/10=16
x=16*10
x=160.