Explanation:
Since density is calculated with mass divided by volume, changing either of these variables will affect the density, not necessarily both of them. If only the volume is increased or only the mass is decreased, the density will decrease. If only the volume is decreased or only the mass in increased, the density will increase.
Example:
Original density is 50g/ml. Mass is 50g and volume is 1ml.
Increase mass only:
mass = 100g
Density = 100g/ml <= Density is increased
Decrease mass only:
mass = 25g
Density = 25g/ml <= Density is decreased
Increase volume only:
volume = 2ml
Density = 50g/2ml = 25g/ml <= Density is decreased
Decrease volume:
volume = 0.5ml
Density = 50g/0.5ml = 100g/ml <= Density is increased
