  In this paper we discuss delta shock interaction problem for a pressureless
gas dynamics system with two different ways of approaching the subject. The
first one is by using shadow wave solution concept. The result of two delta
shock interactions is delta shock with non-constant speed in a general case.
The second one is by perturbing the system with a small pressure term. The
obtained perturbed system is strictly hyperbolic and its Riemann problem is
solvable. We compare a limit of a numerical wave front tracking results as
small pressure term vanishes with the shadow wave solution. Key words: weighted
shadow waves, delta shock waves, wave front tracking, Riemann problem,
interactions
