155. On a plane, there are 10 lines, and among them, there are no parallel lines and through each point of their intersection, exactly two lines pass. How many intersection points do they have?
$\triangle$ Each intersection point is determined by a pair of lines $a$ and $b$ that intersect at this point. Since the order of these lines does not matter, each pair of such lines is a combination - a combination of 10 elements taken 2 at a time. We get:

$$
C_{10}^{2}=\frac{10 \cdot 9}{1 \cdot 2}=45
$$

Answer $: 45$.