$$53 : 10 - (9 : 100 + 0.91)$$
$$5.3 - (0.09 + 0.91)$$
$$5.3 - 1 = 4.3$$
$$4.6 + 0.4 - 0.5 \cdot 0.4$$
$$4.6 + 0.4 - 0.2$$
$$5 - 0.2 = 4.8$$