The diagram shows two straight lines crossing a pair of parallel lines - OCR - GCSE Maths - Question 2 - 2023 - Paper 5

To find the value of angle $a$, we can use the properties of angles formed by parallel lines. Since the sum of angles around a point is 180°, we can calculate angle $a$ as follows:

$a + 125° + 75° = 180°$

Therefore,

$a = 180° - (125° + 75°) = 180° - 200° = -20°$

Since this is impossible, we need to reconsider: angles 125° and $a$ are the interior angles on the same side of the transversal, so:

$a = 180° - 125° = 55°$

Thus,

a = 55° because it is the alternate angle to 125°.