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harrycatcat1

Puzzle for a child

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I have been charged with helping with my 10 year old granddaughters homework but my brain won't work, can you help?

"If seven people meet each other and each shakes hands only once with each others, how many handshakes will there have been?"

If you know, how did you work it out please?👍

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If person number one lines up to shake everyone elses hand .he will shake 6 times .

When person number 2 lines up he shakes 5 times . (As he has already shook number ones hand ) 

3shakes 4 times  etc   

Equals 21 shakes 

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Thanks to everyone 👍👍👍👍

I couldnt just get my head around it, PW comes up with the answer again.

Edited by harrycatcat1

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Tell yer what Harry , how on earth can a ten year old work that one out , I have read it half a dozen times and still no wiser , maybe living in Norfolk we didn't do a lot of hand shaking when we were ten year old :lol:

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It's an old one, the sequence follows the Triangle numbers; 1, 3, 6, 10, 15, 21, 28...

If n is the number of people, then the number of handshakes is given by:

(n(n-1))/2

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1 hour ago, marsh man said:

Tell yer what Harry , how on earth can a ten year old work that one out , I have read it half a dozen times and still no wiser , maybe living in Norfolk we didn't do a lot of hand shaking when we were ten year old :lol:

To be honest I couldn't make head nor tail of it, how the kids do it I don't know 🤔🤔🤔🤔

1 hour ago, Ricko said:

It's an old one, the sequence follows the Triangle numbers; 1, 3, 6, 10, 15, 21, 28...

If n is the number of people, then the number of handshakes is given by:

(n(n-1))/2

😣😣😣😣😣😣🤔🤔🤔🤔🤔

Call me thick but could you please let me know how this works. Genuinely interested 👍

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54 minutes ago, harrycatcat1 said:

Call me thick but could you please let me know how this works. Genuinely interested

n is 7 Number of people therefore 7X6 (n-1) divided by 2 gives 42 div 2  =  21

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1 hour ago, harrycatcat1 said:
7 minutes ago, Yellow Bear said:

n is 7 Number of people therefore 7X6 (n-1) divided by 2 gives 42 div 2  =  21

😣😣😣😣😣😣🤔🤔🤔🤔🤔

Call me thick but could you please let me know how this works. Genuinely interested 👍

There you go Harry , Yellow Bear have simplified it for the likes of us two , our old teacher used to write on my report , must try harder and room for improvement , that is putting it mildly in case of any ten year old children are reading this :lol:

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The pattern of Triangle Numbers:

1

1+2

1+2+3

1+2+3+4

1+2+3+4+5

Etc.

Yellow Bear explained the algebra beautifully!

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20 minutes ago, marsh man said:

There you go Harry , Yellow Bear have simplified it for the likes of us two , our old teacher used to write on my report , must try harder and room for improvement , that is putting it mildly in case of any ten year old children are reading this :lol:

Phew, I don't know how I didn't think of that 🤣🤣🤣🤣🤣🤣

36 minutes ago, Yellow Bear said:

n is 7 Number of people therefore 7X6 (n-1) divided by 2 gives 42 div 2  =  21

Thanks again 👍👍👍👍

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19 hours ago, spurs 14 said:

Blimey that last one made it looked complicated ! I’m for an easy life as was drummed into us K,I,S,S ,         Keep it simple , stupid      Call me old fashioned but pencil an£ paper normally works it out 

  That's OK if you have 5, 10 or maybe 15 people; now do it for 134 people !

The whole point of Algebra is scale/repetition

RS

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