Mathematics: Post your doubts here!

[Dug]

this is w12 paper 61. i did the first part. dont understand the second one. please help. i need help . i am frustrated. thanks.

Lengths of rolls of parcel tape have a normal distribution with mean 75 m, and 15% of the rolls have
lengths less than 73 m.
(i) Find the standard deviation of the lengths. [3]
Alison buys 8 rolls of parcel tape.
(ii) Find the probability that fewer than 3 of these rolls have lengths more than 77 m

ii) Probability of length less than 73 m and length greater than 77 m is the same since they are the same distance from mean. A normal distribution curve is symmetric about its mean.
P(X<73) = P(X>77) = 0.15

Let X represent the number of rolls having length greater than 77 m.
n = 8
p = 0.15
q = 0.85

P(X<3) = P(X = 0) + P(X = 1) + P(X = 2)
P(X<3) = (8C0) (0.85)^8 + (8C1) (0.15)(0.85)^7 + (8C2) (0.15)²(0.85)^6
P(X<3) = 0.895

 

[Tkp]

I have a question

if in pure we were asked to sketch a graph we must draw it using graph paper and by scale????????????
or draw it with our hands and with no scale

no sketch only

 

[Alice123]

https://www.xtremepapers.com/community/members/dug.23386/
I need help with no 2
thanks in advance
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s12_qp_62.pdf

 

[Tkp]

cud u plz do it as i wasnt getting the ans

A+4d =ar(a+4d)/a=r
A+14d=ar2
A+14d=a(a+4d/a)2
A+14d=a(a2+8ad+16d2/a2)
A+14d=a2+8ad+16d2/a
A2+14ad=a2+8ad+16d2 (a2 cancels out)
6ad=16d2
3a=8d

 

[Tkp]

huh? ..i didnt get q3 and for q8(i) how do ukno dat a+b=-1, y not a+b=7?

just put the values as told in the question

a+bcos(2*0)==-1
a+b=-1
a+bcos(2*.5π)=7
a-b=7
now substitute the values
b=-1-a
a-(-1-a)=7
a+1+a=7
2a=6
A=3
B=-4

 

[Tkp]

huh? ..i didnt get q3 and for q8(i) how do ukno dat a+b=-1, y not a+b=7?

what didnt u get in no.3?
i just did the whole thing.check it again and sry i forgot to put 2x in the superscript value

 

[Dug]

https://www.xtremepapers.com/community/members/dug.23386/
I need help with no 2
thanks in advance
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s12_qp_62.pdf

i)
If the two chosen values are the same, Y takes the value 0. If they are not the same, then Y = Larger X - Smaller X.

Hence, the possible values Y can take are 0, 2 and 4.

Now to draw the table, we need the probabilities.

P(Y = 0) = P(X = 2 and 2) + P(X = 4 and 4) + P(X = 6 and 6)
= (0.5)² + (0.4)² + (0.1)²
= 0.42

P(Y = 4) = P(X = 2 and 6) + P(X = 6 and 2)
= (0.5)(0.1) + (0.1)(0.5)
= 0.1

P(Y = 2) = 1 - P(Y = 0) - P(Y = 4)
= 0.48

ii)
E(Y) = 2(0.48) + 4(0.1) = 1.36

 

[Tkp]

nope

 

[Alice123]

i)
If the two chosen values are the same, Y takes the value 0. If they are not the same, then Y = Larger X - Smaller X.

Hence, the possible values Y can take are 0, 2 and 4.

Now to draw the table, we need the probabilities.

P(Y = 0) = P(X = 2 and 2) + P(X = 4 and 4) + P(X = 6 and 6)
= (0.5)² + (0.4)² + (0.1)²
= 0.42

P(Y = 4) = P(X = 2 and 6) + P(X = 6 and 2)
= (0.5)(0.1) + (0.1)(0.5)
= 0.1

P(Y = 2) = 1 - P(Y = 0) - P(Y = 4)
= 0.48

ii)
E(Y) = 2(0.48) + 4(0.1) = 1.36

thanks a lot

 

[Islam Atef]

no sketch only

thx

 

[A star]

haha pretty much the same here.. How's maths for ya.. ? should be pretty easy after last year.. right?

nooo stats is breaking me up

 

[asexamskillme111]

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Mathematics%20(9709)/9709_w11_qp_33.pdf

Q 9 part iii. The marking scheme uses a formula. I can't exactly remember what the formula and I can't find it anywhere. Help anyone?

 

[applepie1996]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s06_qp_3.pdf
could someone please solve question 9 (ii)
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s07_qp_3.pdf
question 2 (ii)
question 7 (ii)
could someone infinity times please do them

 

[applepie1996]

could someone solve these P3 questions ^ ^ ^

 

[Alice123]

https://www.xtremepapers.com/community/members/dug.23386/
please help me with no 6ii? is there any shortcut method? thanks in advance
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w12_ms_62.pdf

 

[Alice123]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w12_qp_61.pdf

Question 2: Explain it as much as you can and solve it completley .. since I don't understand it at all :S

Dug PhyZac and anyone else who has statistics

EDIT: Ah Got It.. It was tricky .. but opening the bracks did the trick...

can u pls solve it?

 

[Dug]

https://www.xtremepapers.com/community/members/dug.23386/
please help me with no 6ii? is there any shortcut method? thanks in advance
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w12_ms_62.pdf

I assume you have used the following method.
3 : 111
4 : 112, 121, 211
5 : 113, 131, 311, 122, 212, 221
6 : 123, 132, 312, 213, 231, 321, 114, 141, 411, 222

You can make it shorter by using permutation.

3 : 3!/3! = 1
4 : 3!/2! = 3
5 : 3!/2! + 3!/2! = 6
6 : 3!/2! + 3!/2! + 3!/2! + 3!/3! = 10

This can be done by intuition alone. I just showed you the working to make you understand. Hope you got it!!

 

[syed1995]

can u pls solve it?

The method i use is very simple.

Just remember two things.

Ex = mean * n
E(number) = number * n

where n is the total number of people or frequency.

n = 24
E(x-36)=-60
Ex-E36=-60
Ex=-60+E36
Ex=-60+(24*36)
Ex=804

E(x-36)^2 = 227.76
E(x^2-72x+1296) = 227.26 (We just opened the square via the (a-b)^2 = a^2 -2ab + b^2
Ex^2-72Ex+E1296 = 227.26
Ex^2=227.76+72(Ex) - E1296
Ex^2=227.76+72(804) - 24*1296
Ex^2=27011.76 or 27000 (3sf)

 

[salvatore]

okay, i'll try to explain.View attachment 22873
First you have to find the length of the blue line. you have to use ' cos' to find it, lets call this line AX
so,
AX= 5c0s0.6 = 4.12 cm
now you will have to find the small length PX. to find PX u need to know the length of AQ, the length of AQ is 5cm because 'BQD' is an arc of a circle with center 'A' so it means its 5cm (the length AQ is the radius of the circle with center A)
so since u know AQ = 5cm, to find PX :
PX = 5 - 4.12 = 0.873 cm
but they are asking us for the length of PQ, so the length is 2*PX
===> PQ = 2*0.837
= 1.75 cm
hope u understood

Thank you so much for the clear explanation

 

[Alice123]

The method i use is very simple.

Just remember two things.

Ex = mean * n
E(number) = number * n

where n is the total number of people or frequency.

n = 24
E(x-36)=-60
Ex-E36=-60
Ex=-60+E36
Ex=-60+(24*36)
Ex=804

E(x-36)^2 = 227.76
E(x^2-72x+1296) = 227.26 (We just opened the square via the (a-b)^2 = a^2 -2ab + b^2
Ex^2-72Ex+E1296 = 227.26
Ex^2=227.76+72(Ex) - E1296
Ex^2=227.76+72(804) - 24*1296
Ex^2=27011.76 or 27000 (3sf)

thanks a lott