Given 21 points on a circle
We know that we require two points on the circle to draw a chord
Number of chords is are
21C2=
\( \dfrac{21!}{2!(21-2)!}=\dfrac{21\times 20\times 19!}{2!\times 19!}\)
= \( \dfrac{21\times 20}{2\times 1}\)
= \( \dfrac{420}{2}=210\)
Total number of chords can be drawn are 210
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