50g of Ice at 00C has a latent heat of
Q=m×L=50×80
=4000cal
Now for water to reach 00C without changing its state
Heat released by water = mCpΔT
= 50×1×20
= 1000cal
As the heat to be removed from water is less than the latent heat of 50g of ice, the resultant mixture stays at 00C temperature.