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The numbers of straight lines can be formed out of 10 points of which 7 are collinear ?
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- 26
- 21
- 25
- None of these
Correct Option: C
If there were no three points collinear. We should have 10C2 lines but since 7 points are collinear we must subtract 7C2 lines and add the one corresponding to the line of collinearity of the seven points.
Thus, the required number of straight lines .
= 10C2 - 7C2 + 1 = 25
