To find out the total cost including a 25% tip in one step, Samir should multiply the cost of the meal by \(1 + 0.25\) (which represents the original meal price plus 25% of it). This can be simplified as:
\[ 1 + 0.25 = 1.25 \]
Therefore, he should multiply the cost of the meal by \(1.25\) to find the total cost including the tip in one step.