11.
Every handshake takes 2. If no one shakes hands twice with another, there are 10+1 total people shaking hands (11).
Name them 1 thru 11. Make a line and 11 goes down the line and shakes 10 hands and then leaves. 10 then shakes 9 hands and leaves. 8 then shakes 7 hands and leaves. Etc. 2 shakes hands with 1 and leaves. 1 just leaves.
11— 10 hs
10— 9 hs
9— 8 hs
8— 7 hs
7— 6 hs
6— 5 hs
5— 4 hs
4— 3 hs
3— 2 hs
2— 1 hs
1— leaves
Total handshakes 55, total people 11.
because 1/2 is equal to 50%
0.5≠50
The answer is 3x+2 over (x+2) (x-2)
The formula for area of a trapezoid is

so you add up the bottom base (17) and the top base (3) to get 20.
you then take the sum of the bases (20) times the height (8) to get 160.
lastly, you take 160 ÷ 2 to get your final answer, which is 80 (: