Mathematics: Post your doubts here!

[peter brown]

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

 

[Manobilly]

Thanks I got the answer

Question number???

 

[MONJUR HASAN NISHAD]

Can someone explain Oct/Nov 2010 Paper 33 question 10 ii b? How the hell can you find the SIX roots? Please help me out!

 

[Khav19]

I really need some help
i am sure its simple but i completely forgot about it

1.Simply
mC3
Answer is m(m-1)/2
Can you show me the working step by step , i am having huge trouble in simplying these where either n or r is unknown

 

[Iffat]

Iffat
i hope this answers ur question for number 10 on the other ppr. where c is the x co-ordinate of the vertex.

thanx soo much

 

[Iffat]

ppl i need ur help
2007 may-jun p1:
q3 and q8(i)

2007 oct-nov p1:
q4(ii),(iii)

2008 oct-nov p1:
q2

 

[Tkp]

ppl i need ur help
2007 may-jun p1:
q3 and q8(i)
for number 3

(1-sin2x/cos2x)/ (1+sin2x/cos2x)
(cos2x - sin2x/ cos2x)/ (cos2x+ sin2x/ cos2x)
(cos2x - sin2x/ cos2x)/(1/ cos2x) cos2x cancels out and we get
cos2x- sin2x then 1- sin2x- sin2x=1-2 sin2x
8(i)
Put the values as told in the question
U will get 1st 1 a+b=-1
2nd one u will get a-b =7
Substitute and u will get the answer

 

[Tkp]

ppl i need ur help

fr the oct nov 07
equal the terms of 1st,4th,and 15 of arithmetic progression to 1,2,3 terms of geometric progression
a+4d=ar
a+14d=ar^2

substitute it and u will get the answer and the 3rd is easy

 

[Islam Atef]

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

 

[Iffat]

fr the oct nov 07
equal the terms of 1st,4th,and 15 of arithmetic progression to 1,2,3 terms of geometric progression
a+4d=ar
a+14d=ar^2

substitute it and u will get the answer and the 3rd is easy

cud u plz do it as i wasnt getting the ans

 

[Iffat]

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

 

[salvatore]

http://papers.xtremepapers.com/CIE/...S Level/Mathematics (9709)/9709_w10_qp_13.pdf
Please help me solve qn no. 8 (ii).. I'm totally confused!
Thanks

 

[Kumkum]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w10_qp_13.pdf
Please help me solve qn no. 8 (ii).. I'm totally confused!
Thanks

okay, i'll try to explain.
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

 

[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