a= schimb dimineata,b=schimb dupa amiaza,c=schimb de noapte
a+b+c=1200
b=2c=>c=b/2
a=b+400
b+400+b+b/2=1200 amplificam
2b/2+800/2+2b/2+b/2=2400/2
5b=2400-800
b=1600:5=320 muncitori in tura de dupa amiaza
c=320:2=160 muncitori in tura de noapte
a=320+400=720 muncitori in tura de dimineata