How to calculate the silhouette coefficient?
a(i) : the average distance between 'i' and all other data within the same cluster (source)

b(i) :  the lowest average distance of 'i' to all points in any other cluster, of which 'i' is not a member (source)

So, from the question, a(i) will be 24 as point 'Pi' belongs to cluster A and b(i) will be 48 as it is the least average distance that 'Pi' has from any other cluster than A (to which it belongs).

So, as a(i) &lt; b(i),  silhouette coefficient s(i) = 1 - 24/48 = 0.5