Handshake and Fencepost

1. You will shake 19 hands.
H = N
N-1=H

2. There will be 13 posts
F = N
F+1=P

3. There will be 45 handshakes for 10 people.
10(10-1)/2 = 45
There will be 190 handshakes for 20 people.
20(20-1)/2 = 190

4. These problems are important to solve because it will help somebody know how to do their job correctly. A carpenter may use these equations to get the proper measurements. A chef may use these equations to cook the correct amount of food for guests. And a teacher may use these equations in everyday math.