Question 1085786
Every person clinks their glasses, acoording to the rule the first person make n-1, the second person has already make the toast with the first person, so he clinks (n-2) times and so, it goes on until the (n-1) person make only one toast.


So total clinks are = (n-1) + (n-2) + (n-3)+... + 1.

So using the formula for an arithmetic progession.

Total Clinks = (n-1+1)(n-1)/2 =(n^2-n)/2.

in this case n=5, so answer is = (5^2-5)/2 = 10.

@natolino_