You are observing a cocktail party that has seven guests. You notice that each guest shakes hands with one another once they meet, but never again. How many handshakes occurred during the cocktail party?

21.

*(7-1) = 42. However, you must remember that once person A shakes hands with person B, person B does not re-shake hands with person A again. Therefore, the solution become (7*(7-1))/2 = 21, or 1+2+3+4+5+6 = 21.

## Comments

Sign uporlog in with Facebookto comment.surya prakash singh7c2 = 21

Majeed Siddiqui21

psyclaudeZI think the answer shall be 8 * (8 - 1) / 2 = 28. Since the question says 'YOU are observing ... has seven guests' therefore there should be 8 people in total...

Sounds like trolling...

jleonardA fun way to solve this, since it's only 7 guests, is to construct a complete graph (k7). Then all you need to do is count up the edges.

AakashInteresting approach. Combinatorics also works nicely.

GuilhermeSimple combination: 7! / ( 2! * (7-2)! )

Anand KumarC(7,2)

pratik3121

Anubhv Yup Pii Moon's1-6 2-5 3-4 4-3 5-2 6-1 count the right side numbers ( 6+5+4+3+2+1)=21

Tarun245the answer is probably something like 21