80 decalitri= 80 x 10=800 litri
a( prima saptamana)=1/5 din 800
b( a doua saptamana)= 2a
c( a treia saptamana)= [800-(a+b)]:2
a=1/5 din 800= (800:5)x1=160x1=160 litri
b=2x160 => b=320 litri
c=[800-(160+320)]:2 => c=(800-480):2 => c=320:2 => c=160 litri
800-160-320-160=160 litri au ramas
Solutia: prima saptamana (a)=160 litri; a doua saptamana(b)=320 litri; a treia saptamana(c)=160 litri
Verificam: a+b+c+restul= 160+320+160+160=800 litri
