Why is it NOT 90?

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How many handshakes occur at a party with 10 people each person shakes the hand of every other person once?
#unitedstates #usa

[@adamnyback]

An easier way to look at this problem: Each person shakes hand with the other 9 people, so we have 10*9. But then we have counted each handshake twice, so we need to divide by 2. Similarly with 20 people, we have 19 handshakes each and divide by 2. 20*19/2=10*19=190

[@alessiovittorio7092]

20!/(2!×18!) = 20×19/2 = 190 The total number of handshakes is 190.

[@MrAtomicPig]

(N×N - N{they can't shake with themselves})/2{they can't shake twice} 🐖

[@xstreamspeed]

If there were 20 people in the room and we had to count the number of handshakes: k = 2 (groups of two people) n = 20 (total twenty people) By using: n!/k!(n-k)! 20!/2!(20-2)! 20!/2(18!) We can rewrite this as: (20 x 19 x 18!)/2 x (18!) | (18! cancels out) 380/2 = 190 handshakes.

[@Jessa-w6e]

20-1=19*20=380÷2=190 Formula is n*(n-1)÷2

[@rahabintemotiul]

The fact that I just learned about this in school today, and youtube recommended this video

[@heenakhandelwal8608]

Thank you sir ❤❤ Your videos help me a lot to understand tough math concepts

[@brain_station_videos]

Appreciate it. 🙏

[@richardslater677]

10 people shake hands 9 times = 90 but each event is 2 handshakes = 45. 20x19=380, 380/2=190. [n(n-1)]/2

[@mattitatti-s5d]

harvard asses cant even slove this no shame I'm 12 years and I loved it

[@RishanAjayFJ]

Amazing and mind-blowing😂😂😂🤯🧠🤯🤯🤯

[@A.I.0101]

The answer to a question about 20 people is 190 handshakes

[@Jessa-w6e]

This is a more easy formula... The formula of handshakes are n*(n-1)÷2.... So 10*9=90÷2=45....

[@ArthPokiya]

I just solved it in 10 seconds and thid method is a lot more amazing and INTUITIVE. First imagine a 10x10 Multiplication Table Square. So, First first row and column will be squares named from 1 to 10. Assume that thise numbers are people. We know that a person would not shake his own hand and that would not count. So Eliminate the squares that contain two same people, or simply eliminate the perfect squares. Then, 90 squares will be remained the the multiplication grid table. And it will be divided into 2 equal parts. But you would see that those two parts are identical. E.g. P1 shaking hnd with P8 is same as P8 shaking hnd with P1 or 1x8 is same as 8x1. But we need a unique handshake, or we need a unique number in the remaining squares. So eliminate the bottom part of the whole squares. Then we would have half of the 90 squares.... 45 squares. And this 45 numbers are unique, they do not repeat in the remaining squares. And there you have it 45 HANDSHAKES!! Edit:- If there were 20 peoples then the total handshakes will be (20^2 - 20)/2 = 190 The general formula is (n^2 - n)/2

[@anandselvamani5093]

Sum = n(n+1)/2 =19(19+1)/2 =19(10) =19

[@brain_station_videos]

You mean 190?

[@anandselvamani5093]

Yes

[@Mohamed.Soltan1991]

Amazing ❤❤

[@Broken_Captain]

I guessed it as, each person will handshake with other person so one person will do 9 handshakes and there's 10 people in room so there should be 10*9= 90 handshakes, but a handshake need to person and it's mentioned that every person do handshake with a person only once, so 90/2= 45 handshakes 😊 Similarly, For next problem, 20*19= 380 and 380/2= 190 handshakes

[@mdahnafalfee169]

0:08 Damn it's 45, easy!

[@bhajan.path123]

Please make a video on multiplication tricks

[@brain_station_videos]

Hi, already made 2 videos on the same

[@shomil_sw]

Use ap summation N/2(a+l) N= 9 A=9 L=1 9/2(9+1) =9x5=45

[@marifkhan2003]

Nice! I have a question? If there are 300 people in a gathering and one shake hand takes 5 second then how much time needed to complete hand shakes. It looks like 2 and half days. Am I correct? And if you just hug each other which might take 10 sec, it means 5 days.

[@rohitkaushik2311]

It is very basic question and i solved it using an A.P series method.

[@Michael-n9d6p]

If counting yourself there's 10 people and each person has a hand shake with half of the people then 5 people shook hands with 5 other people. They're were 10 people shaking hands. There were a total of 5 handshakes If each person had hand shake with 1/2 the people in the room then 10 people shook 5 peoples hands and so there were 50 hand shakes in the room.

[@devparmar3480]

It's 25 I think that 1 man does handshake 9 times than leaves room now another 1 guy does handshake with 7 guys and leaves room It's 9 + 7 + 5 + 3 + 1 = 25 I haven't watched the video so maybe I am wrong Edit : hehe I got it wrong soo bad

[@theplanetofgames]

45 shake hands.

[@YourPalAlRetroGamer]

190 handshakes

[@smarthsurya2146]

10!/2!*8!=45

[@mattitatti-s5d]

bro this is so easy

[@AliAhmed-is2fr]

The "so good" comment is just obnoxious.

[@brain_station_videos]

Soooo Gooood ❤️

[@vibingowsic2338]

As my calculation method n(n-1)/2 20(20-1)/2 10x19 = 190 I forgot the name of this method, can anyone tell me

[@shomil_sw]

Summation of natural number

[@adityamanohar2564]

10c2

[@nabanitachakraborty5537]

190

[@hari-t5r]

we can also say n(n-1)/2 assuming n is the total number of the people

[@Michael-n9d6p]

What if 10 people are in a circle and not in a line

[@Maths_Wonderland]

190

[@bhupeshkarir5928]

190