7th grade Math
posted by Teresa Joseph .
At a faculty costume party, each teacher from transylvania Middle School came dressed as his or her favorite creepy creature. The teachers arrived one at a time, and when a new teacher came in, each of the teachers already there lined up at the door and shook hands with the newcomer. Count Dracula(Mr.Blab) kept track of the number of hand shkes exchanged. He said that there were 171 handshakes exchanged at the party.
How many teachers came to the costume party?

The second teacher would have one handshake, the third, two, and so on. Continue on until you get a sum of 171.
I hope this helps. Thanks for asking. 
1,333,456,676,766,600

The answer is 19. There were 19 teachers at the party.

I think it is 170 because the second person has the first handshake with the new teacher and its like one less.The answer is 170.

i don't get two methods too solve it

I don't get methods too solve problem heeeeeeeeellllllllllllllllp pllllllllllllease