Respuesta :
2 people => 1 handshake (AB)
3 people => 3 handshakes (AB, BC, AC)
4 people => 6 handshakes (AB, AC, AD, BC, BD, CD)
Do you see a pattern here?
We can write a general formula for this
[tex]handshakes=\frac{n\cdot(n-1)}{2}[/tex]Since we are given that there were 15 handshakes
[tex]15=\frac{n\cdot(n-1)}{2}[/tex][tex]\begin{gathered} 2\cdot15=n\cdot(n-1) \\ 30=n\cdot(n-1) \\ 30=6\cdot(6-1) \\ 30=6\cdot(5) \\ 30=30 \end{gathered}[/tex]This means that n = 6 people were present at the party.
You can substitute n = 6 into the above formula and you will notice that it will give 15 handshakes
[tex]handshakes=\frac{n\cdot(n-1)}{2}=\frac{6\cdot(6-1)}{2}=\frac{6\cdot5}{2}=\frac{30}{2}=15[/tex]