Handshakes

How many handshakes would we have to shake in the whole class?                          Number of people(21)

How are we going to do this?

Every person in the five groups shakes each others hands which is 30 altogether.

* * (16)     #  #(12)   @  @(8)   $   $(4)    *   *
* *            #  #         @  @        $   $         *   *     + (20)

one person(each group) from the stars group(and other groups) from above shakes everyone's hand except their own group that continues all around one by one.

So when that is being done one group is

64
48
32
16
20    add all the numbers together then you will get the answer which is 210

then when you add one more person that person shakes everyone's hand then that will be 21 add that to 210 you will get 231.