If 9 persons meet at a reunion and each person shakes hands exactly once with each of the others, what is the total number of handshakes?  Choose the correct choice from the following options.
A) 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
B) 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
C) 9 × 10
D) 36
E) 45
1st person will have 9 handshakes, 2nd will have 8, ....8th will have 1 and 9th will have 0   =8+7+6+5+4+3+2+1= 
<gadget id="calculator">8+7+6+5+4+3+2+1</gadget>
<output>36</output>
36   if we generalize this: if there are n people then there will be n(n-1)/2 handshakes.   Ans.36)
<result>D</result>
If 9 persons meet at a reunion and each person shakes hands exactly once with each of the others, what is the total number of handshakes?