think this way.

assume x values are

(x1,.... x10)

Y values are

(y1,.... y11)

you need three points to form a triangle.

(x1,y1) , (x1,y2) (x2 y1) form a triangle.

--> that means you need to select two points (x1,x2) from x series and two points (y1,y2) from y series.

Select two points from x series = 10P2 (since order does matter.. it should be permuation)

Select two points from y series = 11P2

Answer = 11P2 *10P2 = 11*10 * 10*9 = 9900

I hope you got it.

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