Posted by **Rhegan** on Monday, January 25, 2010 at 8:53pm.

At a party, there were 105 handshakes. If each person shook hands exactly once with every other person, how many people were at the party?

- 7th grade -
**bobpursley**, Monday, January 25, 2010 at 9:04pm
If there are N folks, then

n-1 + N-2 + n-3 +....1 handshakes

take 4 people:

3+2+1= 6 handshakes.

10 people is

9+8+7+6+5+4+3+2+1= 45

14= 13+12+11+ 10 + number above

= 13+12+11+10+45= 91

you want 105, so try

15= 14+ 91

- math -
**Anonymous**, Monday, March 8, 2010 at 7:58pm
So the answer is 15? But still I don't get how you solve it

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