6 points are marked on a straight line and another 5 points are marked on a second straight line with no points in common. How many triangles can be constructed with vertices from among the above points?
Choose the most appropriate option:
A) 21
B) 91
C) 168
D) 196
E) 135
Solution: select 2 from 5 and one from 6 + select 2 from 6 and 1 from 5   5C2*6C1 + 6C2*5C1   = 135   Answer : 135
<result>E</result>
6 points are marked on a straight line and another 5 points are marked on a second straight line with no points in common. How many triangles can be constructed with vertices from among the above points?