Given five line segments of lengths 2, 3, 4, 5, 6 units. Then the number of triangles that can be formed by joining these lines is

We know that in any triangle the sum of two sides is always greater than the third side.

$\therefore$ The triangle will not be formed if we select segments of lengths (2, 3, 5), (2, 3, 6) or (2, 4, 6).

Hence number of triangles formed ${=}^5{\mathrm{C}}_3-3$.