Răspuns:
Explicație pas cu pas:
a=0.2 =2/10 =1/5
b=0.5 =5/10 =1/2
c=0.(3) =3/9 =1/3
d=0.(6) =6/9 =2/3
a=b=c=c=k
a:1/5=k a=k/5
b=k/2
c=k/3
d=2k/3
3a -c +d-b =13
3k/5 - k/3 + 2k/3 -k/2 =13 numitor 30
18k-10k+20k-15k =390
13k =390
k=30
a =k/5 =30/5 =6
b=30/2 =15
c=30/3 =10
d=60/3=20