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JEE Mains · Maths · STD 11 - 6. permutation and combination

Consider a rectangle \(ABCD\) having \(5,7,6,9\) points in the interior of the line segments \(AB,CD , BC , DA\) respectively. Let \(\alpha\) be the number of triangles having these points from different sides as vertices and \(\beta\) be the number of quadrilaterals having these points from different sides as vertices. Then \((\beta-\alpha)\) is equal to :

  1. A \(795\)
  2. B \(1173\)
  3. C \(1890\)
  4. D \(717\)
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Answer & Solution

Correct Answer

(D) \(717\)

Step-by-step Solution

Detailed explanation

\(\alpha=\) Number of triangles \(\alpha=5 \cdot 6 \cdot 7+5 \cdot 7 \cdot 9+5 \cdot 6 \cdot 9+6 \cdot 7 \cdot 9\) \(\quad=210+315+270+378\) \(\quad=1173\) \(\beta=\) Number of Quadrilateral \(\beta=5 \cdot 6 \cdot 7 \cdot 9=1890\) \(\beta-\alpha=1890-1173=717\)
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