edexcel probability and correlation

Original post by Lamalam

can anyone explain the answer to part (d), can a tree diagram or venn's diagram be drawn to help my understanding?

38x8 is husband in one and wife in the the other
32x22 is both in one and neither in the other

Reply 2

BabyMaths

Original post by Lamalam

also, is it true that Sxx and Syy in correlation chapter are always positive values? Why? How about Sxy, why isn't it always having positive value, isn't it related to variance also?

thank you very much! :smile:

S_{xx}=\sum (x-\bar{x})^2 \ge0

because it's a sum of squares.

The same goes for

S_{yy}

.

S_{xy}

on the other hand can be negative since

S_{xy}=\sum (x-\bar{x})(y-\bar{y})

.

Reply 3

the bear

20

yes a Venn diagram would help.

the easiest way i found is to write down the options:

suppose the two couples are Amy & Bert and Yolanda & Zack

the options are:

Amy retired & Bert retired & Yolanda not & Zack not
Amy retired & Bert not & Yolanda not & Zack retired
Amy not & Bert not & Yoland retired & Zack retired
Amy not & Bert retired & Yolanda retired & Zack not

Reply 4

OP

Original post by BabyMaths

S_{xx}=\sum (x-\bar{x})^2 \ge0

because it's a sum of squares.

The same goes for

S_{yy}

.

S_{xy}

on the other hand can be negative since

S_{xy}=\sum (x-\bar{x})(y-\bar{y})

.

umm I dont understand the last sentence, can you explain a bit further ? thank you soo much!!!

Reply 5

OP

Original post by the bear

yes a Venn diagram would help.

the easiest way i found is to write down the options:

suppose the two couples are Amy & Bert and Yolanda & Zack

the options are:

Amy retired & Bert retired & Yolanda not & Zack not
Amy retired & Bert not & Yolanda not & Zack retired
Amy not & Bert not & Yoland retired & Zack retired
Amy not & Bert retired & Yolanda retired & Zack not

how should the venn diagram be drawn? @@

Reply 6

7253567

8

Original post by Lamalam

how should the venn diagram be drawn? @@

A Venn diagram should not be used in this situation because the outcome of one affects the outcome of the other.

Posted from TSR Mobile

Reply 7

OP

Original post by Trouty97

A Venn diagram should not be used in this situation because the outcome of one affects the outcome of the other.

Posted from TSR Mobile

i have no idea how to draw a tree diagram either, can you help me?
:confused:

Reply 8

BabyMaths

Original post by Lamalam

umm I dont understand the last sentence, can you explain a bit further ? thank you soo much!!!

What do you get for

S_{xy}

if you have y=1 when x=3 and y=3 when x=1?

Reply 9

Original post by Lamalam

how should the venn diagram be drawn? @@

You have a suitable venn diagram in the original post

Reply 10

Original post by Lamalam

i have no idea how to draw a tree diagram either, can you help me?
:confused:

Why do you need one

Using the info in your OP

What is the P(couple A are both retired and couple B are neither retired)

Reply 11

the bear

20

Original post by Lamalam

how should the venn diagram be drawn? @@

the diagram is for one couple only: the left hand circle is "husband retired", the right hand "wife retired".

because there are 2 couples you need to consider 2 of these diagrams, combining probabilities from the first couple AND ( clue !!! ) the second couple

Reply 12

OP

Original post by TenOfThem

Why do you need one

Using the info in your OP

What is the P(couple A are both retired and couple B are neither retired)

.32*.22?

Reply 13

OP

Original post by TenOfThem

Why do you need one

Using the info in your OP

What is the P(couple A are both retired and couple B are neither retired)

0.32*0.22?

Reply 14

Original post by Lamalam

0.32*0.22?

yes

And what is the P(just the husband in one set AND just the wife in the other set)

OP

0.38*0.08?

OP

Original post by TenOfThem

yes

And what is the P(just the husband in one set AND just the wife in the other set)

\
0.38*0.08?

Reply 17