## sasogeek 4 years ago It was Helen's first day at school. The teacher suggested that it would be a good idea for each child to meet every other child in the class. The teacher said, "When you meet, please shake hands and introduce yourself by name." If there were 10 children in the class, how many total handshakes were there?

1. anonymous

Don't you want to challenge me? :P

2. ash2326

This is just like selecting any two people out of 10 = 10C2 or 45

3. sasogeek

LOL soon ffm

4. anonymous

$$\Huge \frac{n\times (n-1)}{2}$$

5. anonymous

Yes, 45. It is like 1+2+3+....+9.

6. anonymous

$$\Huge\sum \limits_{i=1}^{n-1} i$$