If 5a + 3b : 2a - 3b = 23 : 5, then the value of a : b is

$$\eqalign{ & = \frac{{5a + 3b}}{{2a - 3b}} = \frac{{23}}{5} \cr & \Rightarrow 5\left( {5a + 3b} \right) = 23(2a - 3b) \cr & \Rightarrow 25a + 15b = 46a - 69b \cr & \Rightarrow 21a = 84b \cr & \Rightarrow \frac{a}{b} = 4. \cr & {\text{Hence}},\,a:b = 4:1 \cr} $$