If $3\dfrac{1}{2}$ litres of milk costs ₹49, find the cost of one litre of milk?

Let the cost of one litre of milk be ₹$x$.

$3\dfrac{1}{2} \times x = 49\\[1em] \Rightarrow \dfrac{7}{2} \times x = 49\\[1em] \Rightarrow x = 49 ÷ \dfrac{7}{2}\\[1em] \Rightarrow x = 49 \times \dfrac{2}{7}\\[1em] \Rightarrow x = \dfrac{49 \times 2}{1 \times 7}\\[1em] \Rightarrow x = \dfrac{98}{7}\\[1em] \Rightarrow x = 14$

The cost of one litre of milk = ₹14.