00:01
In this question, we're given that there are 153 handshakes that took place at a party, and each person should hands exactly once with everyone else, and we want to determine the number of people at a party.
00:13
For instance, if there are five people, so person one will shake hands with person two, three, four, and five.
00:24
And person two will shake with three, four, and five.
00:29
And person three will shake with four and five.
00:34
Now you cannot have two because already three and two are over here.
00:39
So basically you do not go back to the same person you shake hands with.
00:44
And for person four, he'll shake hand with five.
00:48
Now if you count, there will be one, two, three, four, five, six, seven, eight, nine, ten.
00:53
So that is actually five choose two.
00:56
So suppose i have n to be the number of people at the party.
01:01
Then, n choose 2 will be equals to 153 handshakes...