Consider the reaction 2A+B+3C  $\to$ P+2Q starting with 3mol of A, 2mol of B and 6mol of C, number of moles of products P and Q produced would respectively be 

Given reaction is 2A+B+3C $\to$P+2Q limiting reagent is calculated by dividing the no. of moles given of each substance by its stoichiometric coefficient. The one with least value is the limiting reagent. Calculation should be done according to limiting reagent. Here the limiting reagent is ‘A’.
2 mole of A =1 mole of P                     $3\text{mole of}\mathrm{A}-?=\frac{3}{2}=1.5\text{mole of }\mathrm{P}$
2 mole of A = 2 mole of Q                     $3\text{mole of }\mathrm{A}-?=\frac{3}{2}\times 2=3\text{mole of }\mathrm{Q}$