A fluid is heated from $40^{\circ}C$ to $60^{\circ} C$ in a countercurrent, double pipe heat exchanger. Hot fluid enters at $100^{\circ}C$ and exits at $70^{\circ}C$. The log mean temperature difference, i.e. LMTD (in $^{\circ}C$), is _____ (round off to $2$ decimal places).