$$\text{Pb(NO}_3)_2 + 2\text{KI} \rightarrow \text{PbI}_2 + 2\text{KNO}_3$$
Source: Chemical Reactions and Equations, Section 1.1.2
Check atom count: Pb=1, N=2, O=6, K=2, I=2 on both sides — equation is balanced by placing coefficient 2 before KI and 2 before KNO₃. The formulae of compounds must not be changed; only coefficients are adjusted (hit-and-trial method).