In this paper,we investigate the packing parameters in graphs.By applying theMantel’s theorem, we give upper bounds on packing and open packing numbers of triangle-free graphs along with characterizing the graphs for which the equalities hold and exhibit sharp Nordhaus–Gaddum type inequalities for packing numbers. We also solve the open problem of characterizing all connected graphs with ρo(G) = n − ω(G) posed in Hamid and Saravanakumar (Discuss Math Graph Theory 35:5–16, 2015).
