How many chords can be drawn through 21 points on a circle? - Vidyadip

Question

How many chords can be drawn through 21 points on a circle?

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Answer

There are 21 points on the circumference on a circle. Since one and only one chord can be drawn by joining 2 distinct points, the required number of chords is given by
${21_{{C_2}}} = \frac{{21!}}{{2!19!}} = \frac{{21 \times 20 \times 19!}}{{2 \times 19!}} = 210$

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