see the following case;
A hunter has a machine gun that can fire 50 gram bullets with a velocity of 150m/s.A 60 kg tiger pounces at him with a velocity of 10m/s.how many bullets should the hunter fire per second into he tiger to stop him in his track.
Here in the hint of question it is given that to stop the tiger ,rate of change of linear momentum of tiger =rate of change of linear momentum of bullet.But I want to ask that why it is necessary to be the linear momentum of both to be same.Please explain me clearly

There's a fundamental concept in physics that says the momentum of a system is constant. Hence any momentum gained by one part of a system (the tiger) must be offset by losses in the momentum of another part of the system (the bullets). Stated another way: the magnituide of change of momentum of both parts is the same.