In the figure a rectangle, a circle and a triangle overlap. What is the sum of the numbers that lie inside the triangle but outside the circle?

Inside the triangle and outside the circle: 8 (triangle only) and 2 (triangle and rectangle). Sum $=8+2=10$. 31 adds every number in the triangle, 25 adds the 15 that is inside the circle too, and 14 takes the triangle numbers outside the rectangle instead.