Answer:
10
Step-by-step explanation:
This is called a combination. Imagine you draw a figure, with a number representing each person, as shown below:
1 2 3 4 5
Person 1 can shake person 2, 3, 4, and 5's hands, for a total of 4 handshakes.
Person 2 can shake 3, 4, and 5's hands, for a total of 3 handshakes.
Person 3 can shake 4 and 5's hands, for a total of 2 handshakes.
Person 4 can only shake 5's hand, which is 1 handshake.
Last you add up the handshakes from every person, 4+3+2+1, which is equal to ten unique handshakes.
