Question 972909
Since each one of the 7 shook 6 hands,
there were {{{6*7}}} ordered pairs of matrons shaking hands,
but those ordered pairs include each handshake counted 2 times:
as person A shaking the hand of person B, and
as person B shaking the hand of person A.
So the number of handshakes is {{{6*7/2=21}}} .