DAY 19

Comment

The largest blue triangle is a quarter of the largest triangle.
The next largest blue triangle is a quarter of a quarter, ie a sixteenth; and so on. So P is represented by the infinite series of blue triangles.

Answer

1/3.

Readers' methods

Helen B, of Berlin:
The three sets of coloured triangles will each cover one third of the total area.

Year 6CW, Twickenham TW2:
In each horizontal part the shaded triangle is one third (of it and the two white triangles),
and so on.
So the total shaded is one third of the triangle.