Metallic copper reacts with a solution of silver nitrate to form a solution of copper(II) nitrate and the silver is precipitated. The equation for this reaction can be written as Cu + AgNO3 ---> Cu(NO3)2 + Ag.
This equation is not yet balanced as the number of atoms of all the elements is not the same on both the sides.
The equation can be balanced by first making the number of AgNO3 atoms on the left equal to two to balance the NO3 ions. As this doubles the number of Ag atoms, they have to be increased on the right hand side also. The balanced equation of Cu reacting with AgNO3 is
Cu + 2AgNO3 ---> Cu(NO3)2 + 2Ag