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Question -

There are 10 points in a plane of which 4 are collinear. How many different straight lines can be drawn by joining these points.



Answer -

Given:

Total number of points= 10

Number of collinearpoints = 4

Number of lines formed= (total no. of lines formed by all 10 points) – (no. of lines formed bycollinear points) + 1

Here, 1 is addedbecause only 1 line can be formed by the four collinear points.

10C2 – 4C2 +1

By using the formula,

nCr = n!/r!(n – r)!

= 90/2 – 12/2 + 1

= 45 – 6 + 1

= 40

 The total no. ofways of different lines formed are 40.

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