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Family ties

Thu 24 Nov, 2005 10:31 am
How big is the chance that the father of my granddad, the same person is as the grandad of my father?

Whim
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Type: Discussion • Score: 1 • Views: 947 • Replies: 10
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material girl

1
Thu 24 Nov, 2005 10:33 am
100% chance, I even wrote out a family tree to make sure.
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Lord Ellpus

1
Thu 24 Nov, 2005 10:33 am
50-50, I would say, as the father of your grandad could come from your Mothers line of ancestors.
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markr

1
Thu 24 Nov, 2005 12:44 pm
I question the uses of the definite article "the" instead of the indefinite article "a."

Your father has two granddads, and you have two granddads who each have a father. There are a total of three men involved in the problem because one man fits both descriptions.

If you select one of these men at random, the probability is 1/3 that he fits both descriptions.

If you randomly select the father of one of your granddads, the probability is 1/2 that he is a granddad of your father.

I'm not sure what the riddle is asking for.

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vinsan

1
Fri 25 Nov, 2005 03:25 am
Re: Family ties
whimsical wrote:
How big is the chance that the father of my granddad, the same person is as the grandad of my father?

Whim

X is a person .... So

F(x) = X's Father

M(x) = X's Mother

Function G(X) = Grandfather of X

G(X) = {F(F(X)), F(M(X))} -------------- EQ I

So it has Set of following Solutions where U represents urself

G(U) = { F(F(U)), F(M(U)) }

So the Father of ur Grandad G(U) is

F(G(U)) = { F(F(F(U))), F(F(M(U))) } ---------- Case I (Father of ur Granddad}

Using (EQ I) we have Granddad of ur Father is where X is replaced by ur Father i.e F(U)

G(F(U)) = {F(F(F(U)), F(M(F(U))) } ---------- Case II (Grandad of ur Father)

F(F(F(U))) is the common person ----------------Using Case I and Case II

..... So we have 3 entities F(F(F(U)), F(M(F(U))), F(F(M(U))) to choose the single person F(F(F(U))) from.

Probability(ur question) = 1/3
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Lord Ellpus

1
Fri 25 Nov, 2005 04:59 am
Re: Family ties
whimsical wrote:
How big is the chance that the father of my granddad, the same person is as the grandad of my father?

Whim

So, basically, we are looking for how many Great Grandads are available to each statement.

2. Father of my grandad.........Follows BOTH Paternal AND Maternal lines, as one of "my grandads" could be my MUMS dad.

So, therefore, the chances of 1(....from one line) being the same as 2 (......from two lines) = 1 in 2, which = 50%.

Looking at it logically, the difference between the statements 1 and 2 is that:-

In total, there are TWO Great grandads available at the top of the chain in statement 1. (Paternal line only)

....But there are FOUR Great grandads at the top of the chain in statement 2. (Both lines to be considered).

It therefore comes out as a 2 in 4 chance, ie 50%.
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Lord Ellpus

1
Fri 25 Nov, 2005 05:08 am
A similar brain teaser for you.......

Two humans bump into each other unexpectedly in the High Street.

One is the Father of the other one's son.

What is their family connection?

Please PM me with the answer, as it may be obvious to some, but a little trickier to others, so it would be good to keep the question officially unanswered for a short while.

I will list those who gave the correct answer in a couple of days.
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Lord Ellpus

1
Fri 25 Nov, 2005 05:31 am
My earlier statement is wrong, but as I can't edit it, I will have to rectify this here......

" ....But there are FOUR Great grandads at the top of the chain in statement 2. (Both lines to be considered). "

....But though there are still TWO relevant Great grandads at the top of the chain in statement 2. (Both lines to be considered), only one of those can be related to my father, as the other one tracks the maternal line.

So therefore, the 1 in 2 chance still stands.

(I hate this edit button lark, as I shot myself in the foot by entering another post soon after the error........Bah!)
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Lord Ellpus

1
Fri 25 Nov, 2005 05:35 am
.....Ilegal interbreeding notwithstanding, of course!
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vinsan

1
Fri 25 Nov, 2005 06:15 am
Re: Family ties
Lord Ellpus wrote:
whimsical wrote:
How big is the chance that the father of my granddad, the same person is as the grandad of my father?

Whim

So, basically, we are looking for how many Great Grandads are available to each statement.

2. Father of my grandad.........Follows BOTH Paternal AND Maternal lines, as one of "my grandads" could be my MUMS dad.

So, therefore, the chances of 1(....from one line) being the same as 2 (......from two lines) = 1 in 2, which = 50%.

Looking at it logically, the difference between the statements 1 and 2 is that:-

In total, there are TWO Great grandads available at the top of the chain in statement 1. (Paternal line only)

....But there are FOUR Great grandads at the top of the chain in statement 2. (Both lines to be considered).

It therefore comes out as a 2 in 4 chance, ie 50%.

It should be 1/3 ... see my previous post.
0 Replies

230891lc

1
Sat 14 Jan, 2006 09:07 am
i agree with lord it is 50-50 because.

Tom- my father Denise- my mother

The father of my grandad could be peter or Simon.
The grandad of my father is deffiently peter.
So it 50-50
0 Replies

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