SOLUTION: Four lines on the plane have at most N common points. Find N. A)7 B)6 C)5 D)4

Think about it ... imagine drawing the lines one at a time:



The first line has no lines to cross.  Common points = 0.



The 2nd line can cross the first line (at most) once.  Common points = 1.



The 3rd line can cross each of the first two lines once.  That's two more.  Common point count is now 1+2 = 3.



The 4th line can cross each of the first three lines once.  That's three more. Common point count is now 3+3 = 6.



B) 6