Question

Making Triangles
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9 points are marked on a straight line and 7 points are
marked on another line which is parallel to the first line.
How many triangles can you make by joining these
points?​

Answer 1

Triangle is formed by picking 3 point 2 from 1  

st

 line and 1 from 2  

nd

 of 1 point from 1  

st

 line or 2 from 2  

nd

 i.e.

⇒  

10

C  

2

​  

×  

11

C  

1

​  

+  

10

C  

1

​  

+  

11

C  

2

​  

 

=  

2!8!

10!

​  

×  

1!10!

11!

​  

+  

1!9!

10!

​  

×  

2!9!

11!

​  

 

⇒45×11+10×55

=495+550=1045

I hope this helps u

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