A level Statistics doubt??Post your doubts here!

[Kangxidi]

so much anger
a) keep one boy and one girl as one unit you will have 8 blocks left which can change places hence 8!
and then boy and girl can also change place hence 2!
multiply 8! x 2!
b) take one side as noy and other as girl
only one boy can be at one side hence 4C1 and on side one girl 5C1
and then take factorial of children left makes
4 x5 x 7!

I think I read the question of a) wrongly

But why do we take one side boy and one side girl? I thought both sides should be same gender?

 

[A star]

*EDIT* star explained it first, we have different approaches don't look at mine haha I'm weak in permutations

a) Imagine you have 4 boys.

You will have B B B B

And you have 5 girls.

It says that you have to make them alternating (BGBGBGBG) and so on, because a boy must be next to a girl (who in turn has to be next to a boy and so on)

Let's "insert" the girls into the line of boys we have, we will notice that we can "insert" them in 5 different places.

| B | B | B | B |

| = place where we can "insert" the girls.

Since we have only 5 girls (which perfectly fits the slot) we can use 5P5 (or 5!) for the girls.

Since there are 4 different boys, we can use 4!

Therefore 5! * 4!

[There is a simpler explanation on grouping them and stuff, but I prefer explaining this way as it is much easier to be told over the net ]

b) We have two cases for this, the first case being that it's both a boy, and obviously second is that both a girl.

Let's look at first case:

B _ _ _ _ _ _ _ B and a remainder of 5 girls and 2 boys. Since it does not matter how they are arranged inbetween the boys, and that each person are different, we can use 7!.

Second case:

G _ _ _ _ _ _ _ G and a remainder of 3 girls and 4 boys. Same concept applies, 7!.

Therefore 7! + 7! or 7! * 2

Correct me if I'm wrong, again.

i think you misread the question all people do not need to be side by side only particular ones

 

[Kangxidi]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w11_qp_61.pdf
can anyone solve 5(i) ? I get 7.717 for the SD but marking scheme gave 6.38

X~N(20,sd^2)

P(20 - 12 < X < 20 + 12) = 0.94
P(8<x<32) = 0.94

From here it's all calculation, see if it is correct.

 

[Kangxidi]

i think you misread the question all people do not need to be side by side only particular ones

I think I did haha thanks for actually replying

 

[syed1995]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w11_qp_61.pdf
can anyone solve 5(i) ? I get 7.717 for the SD but marking scheme gave 6.38

i) P(20-12<X<20+12)
P(8<X<32)=0.94
P(-12/SD<X<12/SD)=0.94
2Phi(12/SD)-1=0.94
2Phi(12/SD)=1.94
Phi(12/SD)=0.97
12/SD=invPhi(0.97)
12/SD=1.881
SD=6.38

And take it from there in part i...

 

[A star]

I think I read the question of a) wrongly

But why do we take one side boy and one side girl? I thought both sides should be same gender?

look heres it

B1 G1 X X X X X X X
now you need the first two side by side make them one unit that makes 8 groups
take their factorial now we have another posibility
B1 G1 and G1 B1 hence 2!
multiply
8! x 2!

 

[A star]

I think I did haha thanks for actually replying

ITS AN o LEVEL QUESTION DID IN ADDMATHS

 

[Kangxidi]

look heres it

B1 G1 X X X X X X X
now you need the first two side by side make them one unit that makes 8 groups
take their factorial now we have another posibility
B1 G1 and G1 B1 hence 2!
multiply
8! x 2!

Yes thats for part A I clearly understood it thanks!

But what about part B? I thought it's asking to have both end sides to be on the same gender?

 

[syed1995]

ITS AN o LEVEL QUESTION DID IN ADDMATHS

ADDMATHS is the reason why I find P and C comparatively easy as compared to my friends even though Addmaths ruined my O level marksheet It did do some benefit... PS I STILL DON'T KNOW WHAT RELATIVE VELOCITY IS :\

 

[felicia tan]

i got it now. THANKYOU SO MUCH!!

 

[A star]

ADDMATHS is the reason why I find P and C comparatively easy as compared to my friends even though Addmaths ruined my O level marksheet It did do some benefit... PS I STILL DON'T KNOW WHAT RELATIVE VELOCITY IS :\

you will next year
naa i got an A

 

[Alice123]

ADDMATHS is the reason why I find P and C comparatively easy as compared to my friends even though Addmaths ruined my O level marksheet It did do some benefit... PS I STILL DON'T KNOW WHAT RELATIVE VELOCITY IS :\

u wnt need dem fr the rest of yr life

 

[sma786]

How is everyone's preparation for Stats?
I hope everyone get's and A !
I have a doubt,
http://papers.xtremepapers.com/CIE/...S Level/Mathematics (9709)/9709_w12_qp_62.pdf ,Question 2 (ii), how did we find 'p' ? Why will we take normal.d of 0 for p?

 

[sma786]

you will next year
naa i got an A

lol i dont know who you are, but i love those clapping people in your messages

 

[A star]

lol i dont know who you are, but i love those clapping people in your messages

thankyou too stranger
every body does

 

[Kangxidi]

How is everyone's preparation for Stats?
I hope everyone get's and A !
I have a doubt,
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w12_qp_62.pdf ,Question 2 (ii), how did we find 'p' ? Why will we take normal.d of 0 for p?

Work out the probability that the company is making a loss.

Since loss means a profit that is less than zero, we are working P(X<0)

Therefore P(Z < -6.4/5.2) = 1- 0.8909 = 0.1091 <-- probability that it makes a loss.

Next step, a loss of exactly 1 out of 4 days can be modelled with binomial.

X~B ( 4, 0.1901 )

P(X=1)

4C1 * 0.8909^3 * 0.1901

Should give you the answer.

 

[sma786]

thankyou too stranger
every body does

lol you're welcome

 

[sma786]

Work out the probability that the company is making a loss.

Since loss means a profit that is less than zero, we are working P(X<0)

Therefore P(Z < -6.4/5.2) = 1- 0.8909 = 0.1091 <-- probability that it makes a loss.

Next step, a loss of exactly 1 out of 4 days can be modelled with binomial.

X~B ( 4, 0.1901 )

P(X=1)

4C1 * 0.8909^3 * 0.1901

Should give you the answer.

ok but i dint get the part "Since loss means a profit that is less than zero, we are working P(X<0)"

 

[A star]

ok but i dint get the part "Since loss means a profit that is less than zero, we are working P(X<0)"

actually the no mentioned is the profit so u cannot be in loss

 

[Kangxidi]

ok but i dint get the part "Since loss means a profit that is less than zero, we are working P(X<0)"

The original normal distribution is modelled with a mean PROFIT of 6.4 and the PROFIT's standard deviation = 5.2

How do we call a loss then? Loss is when the profit value is less than 0.

Imagine you are buying a can of Pepsi for 3 dollars and sell it for 7 dollars to your friend, your profit is 7-3 = 4 dollars
Imagine you are buying a can of Pepsi for 3 dollars and sell it for 1 dollar to your friend, your profit is 1-3 = -2 dollars (which as we can say, a loss)

Therefore loss is any negative profit i.e. profit of <0