Adding Fractions · Hard problem

Noah subtracted $6\dfrac{1}{5} - 2\dfrac{3}{5}$ and got $4\dfrac{2}{5}$ by subtracting the whole numbers ($6 - 2 = 4$) and then subtracting the fraction parts in whichever order gave a positive result ($\dfrac{3}{5} - \dfrac{1}{5} = \dfrac{2}{5}$), without checking whether borrowing was needed. What is the correct difference?