vshaunak@gmail.com wrote:

There are four points in line L and five points in line P, where L is parallel to P. By linking the 9 points, how many triangles can be formed?

1. 76

2. 20

3. 70

4. 66

5. 80

3. 70

--x---x---x---x----x-- Line P

---x----x----x----x--- Line L

From Line P we have to link 2 points plus 1 of line L to form a tringle, so we have from Line P a Combination of 5,2 times 4 possibilities in line L, sorry if the notations are not that the one you guys know:

C(5,2)*4=( 5!/ ( (5-2)!*2!) ) *4 = ( 5*4 / 2 )*4 =40

Similarly from Line L

C(4,2)*5 = ( 4*3/2 )*5 = 30

Summing the two lines 30+40 = 70