How to calculate 1/a - 2/b 2/a - 1/b where is "divided by"

How to calculate ( 1/a - 2/b ) / ( 2/a - 1/b )

$$\dfrac{ ( \frac{1}{a} - \frac{2}{b} ) } { ( \frac{2}{a} - \frac{1}{b} ) }\cdot \left( \dfrac{ab}{ab} \right) \\\\\\ = \dfrac{ ( \frac{1}{a} - \frac{2}{b} ) \cdot ab} { ( \frac{2}{a} - \frac{1}{b} ) \cdot ab }\\\\\\ = \dfrac{ ( \frac{1}{a}\cdot ab - \frac{2}{b}\cdot ab ) } { ( \frac{2}{a}\cdot ab - \frac{1}{b}\cdot ab ) }\\\\\\ = \dfrac{ ( b- 2a) } { (2b - a) }\\\\\\$$

p-4/p + 16/5p - 1/5 =?

Get the LCM of a and b which is ab then divide accordingly. You should get ((b-2a)/ab) / ((2b-a)/ab) then after cancelling ab on both sides, you remain with (b-2a) / (2b-a)