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For everyone to shake hands with everyone else, there are 21 handshakes.

(below copied from my answer of a similar question)

This is an arithmetic progression and can be solved with the equation Sn=(1+(n-1))(n-1)/2 where Sn is the total sum of handshakes for n people.

NB: I have used n-1 instead of n in the equation for the sum of an arithmetic progression, because you're not really going to shake hands with yourself, so you don't include the nth term, in this case 7.

Alternatively, you can solve this geometrically by drawing a heptagon, drawing lines between all the vertices, and then adding all the lines up.

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Q: Seven people shake hands once how many times do they shake hands?
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How many hand shakes would take place if 20 people shake hands once?

First person shakes hands 19 times, second person 18 etc, a total of 190.


If There are 5 people at a party Each person must shake hands once with every other person at the party How many handshakes does it take to do this?

10 times


How many times does the clock form right angle if the time is 325-600?

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What is the fuedel pyramid?

a way of ranking people in feudal times (medieval europe)


What times on a clock form a straight line?

Starting with the hands in a straight line on the same side of the centre, consider how the hands move: At 12 o'clock they are in a straight line on top of each other. In 1 hour, the minute hand has moved a full circle, but the hour hand has moved forward a bit, so they are in a straight line again when the minute hand a moved a bit more. This will be repeated for each hour, but when the hour hand reaches the 12 again, the hands will have been in line 11 times in the 12 hours. So the hands are in line every 12/11 hours, or 1 hour 5 mins 27 3/11 seconds, giving the times as (rounded to nearest second): 12:00:00, 1:05:27, 2:10:55, 3:16:22, 4:21:49. 5:27:16, 6:32:44, 7:38:11, 8:43:38, 9:49:05, 10:54:33 When considering the hands in line on opposite side of the centre similar logic can be applied as before and so it is known that the hands will line up every 1 hour 5 mins 27 3/11 seconds, thus when the hands are lined up opposite the centre, the times will be (to the nearest second): 6:00:00, 7:05:27, 8:10:55, 9:16:22, 10:21:49, 11:27:16, 12:32:44, 1:38:11, 2:43:11, 3:49:05, 4:54:33

Related questions

If 7 people meet each other and each of the others shake hands 1 time how many times will each have shaked hands?

21 times


How many handshakes if 25 people shake hands with every other person in room?

Each person will shake hands with every other person, except himself. If there are 25 people, each person will shake hands with 25-1 people, or 24. The number of times each person will shake hands with another, will be 25x24. The number of handshakes will be half of that, as each handshake is between two persons. The formula, in other words, is x(x-1)/2, where x is the number of people. With 25 people, it will be 25x24/2 = 300 handshakes.


How do you teach dogs to shake hands?

Go to images and find dogs shaking hand then try. Say shake hands. hold your dogs paw for a while. Do it a few times a day.


How many hand shakes would take place if 20 people shake hands once?

First person shakes hands 19 times, second person 18 etc, a total of 190.


If There are 5 people at a party Each person must shake hands once with every other person at the party How many handshakes does it take to do this?

10 times


How many hand shakes are needed for 10 people?

90. Each person must shake the hand of 9 other people, and there are 10 people. 10 people, each shaking hands 9 times = 90 handshakes.


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Why do you shake hands after a football match?

There is nothing saying they cant shake hands, generally speaking unlike in other sports, only 1 team is on the playing area when the game ends. The winning team usually takes to the field to "celebrate" or shake hands with one-another. Also in baseball unlike in other sports you play the same team 3-4 days in a row and will play some teams in your division 18-19 times in a season. Although baseball players don't take the field to shake hands after a game or series, you will sometimes see a waive or a 'tip of the cap' coming from one dug out to the other, this gesture is the equivalent to a handshake in other sports


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Do African people greet each other by kissing?

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Why do the French kiss each other three times on the cheeks?

Kissing on each cheek is the customary way of greeting in France, just like how Americans shake hands or hug.


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