Question

I don't know this question

Answer 1

lets say there are n persons
first person shakes hand with everyone else: n-1 times(n-1 persons)
second person shakes hand with everyone else(not with 1st as its already done): n-2 times
3rd person shakes hands with remaining persons: n-3
So total handshakes will be = (n-1) + (n-2) + (n-3) +…… 0;
= (n-1)*(n-1+1)/2 = (n-1)*n/2 = 45
= n^2 -n = 90
=(n-10)(n+9) = 0;
= n = 10 OR n =-9
-9 is ruled out so the answer is 10 persons.