Va rog frumos 19 (a ) VA ROGGGG!!

0,5=5/10
2/3:(5/10+5/10*1/3)=2/3:(5/10+5/30)=
2/3:(1/2+1/6)(am simplificat cu 5)=
2/3:(3/6+1/6)=2/3:4/6=2/3*6/4=12/12=1
Seara placuta!:)