Mathematics: Post your doubts here!

[Edison Weeho]

it's because you selected one person already, so the total number is 193 when you select the second one (tree diagram without replacement might help you in this case or use combinations)

oh, thank you, I thought it was to use Binomial distribution ...

 

[Amy Bloom]

Hey everyone!
I have a question which is confusing me, can anyone answer that for me... explain me the steps to go thru.
In a group of 100 people, 40 own a cat, 25 own a dog and 15 own a cat and a dog. Find the probability that a person chosen at random:
(i) owns a dog or a cat [Answer: 0.5]
(ii) owns a dog or a cat but not both [Answer 0.35]
(iii) owns a dog given he owns a cat [Answer 0.375]
(iv) does not own a cat given that he owns a dog [Answer 0.4]
Thank you

 

[Meleko]

Hey everyone!
I have a question which is confusing me, can anyone answer that for me... explain me the steps to go thru.
In a group of 100 people, 40 own a cat, 25 own a dog and 15 own a cat and a dog. Find the probability that a person chosen at random:
(i) owns a dog or a cat [Answer: 0.5]
(ii) owns a dog or a cat but not both [Answer 0.35]
(iii) owns a dog given he owns a cat [Answer 0.375]
(iv) does not own a cat given that he owns a dog [Answer 0.4]
Thank you

in statistics "A or B" means "A or B or both"
P(A or B)=P(A)+P(B)-P(A and B)
P(A given B) = P(A|B)= P(A and B)/P(B)
so P(D)=0.25, P(C)=0.4, P(C and D)=0.15
i) P(D or C)=0.25+0.4-0.15=0.5
ii) P(D or C but not both)=0.5-0.15=0.35
iii)P(D|C)=P(D and C)/P(C)=0.15/0.4=0.375
iv) P(C`|D)=0.1/0.25=0.4 as 25 have dogs and 15 have both --> 10 have a dog but don't have a cat, so P(C` and D)=10/100=0.1

 

[weefeiya]

Was it from variant 2 ?

no, variant 3.

 

[Charlotte20102013]

Hi all. Can someone help me with this
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w11_qp_62.pdf
Q4(i) Why is the answer '45-50' instead of '45-49'? Because the < sign does not have equal sign
Q4(iv) Shouldn't we use Class boundaries in x-axis to draw the graph?
Mark scheme: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w11_ms_62.pdf

 

[Meleko]

Hi all. Can someone help me with this
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w11_qp_62.pdf
Q4(i) Why is the answer '45-50' instead of '45-49'? Because the < sign does not have equal sign
Q4(iv) Shouldn't we use Class boundaries in x-axis to draw the graph?
Mark scheme: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w11_ms_62.pdf

you have a cumulative frequency table, so the values given there are representing the upper bounds of each interval
q4i - the interval is 45 to 50 (45≤median<50)
q4iv - the class boundaries as used

 

[Charlotte20102013]

you have a cumulative frequency table, so the values given there are representing the upper bounds of each interval
q4i - the interval is 45 to 50 (45≤median<50)
q4iv - the class boundaries as used

I still don't really get it...
Another example: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s11_qp_63.pdf
Q3(iii) Why is the midpoint calculated as 4.5 =(9+0)/2 and not 5 =(10+0)/2 ? Since the given info is already the boundaries, shouldn't we calculate midpoint from the boundaries?
Mark scheme: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s11_ms_63.pdf

Another example: http://freeexampapers.automaticpapers.com/as-a-level/mathematics-9709/9709_s14_qp_62.pdf
Q6(iii)
Mark scheme: http://freeexampapers.automaticpapers.com/as-a-level/mathematics-9709/9709_s14_ms_62.pdf

The ways to get midpoints for these two questions are different.. How come?

 

[Meleko]

I still don't really get it...
Another example: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s11_qp_63.pdf
Q3(iii) Why is the midpoint calculated as 4.5 =(9+0)/2 and not 5 =(10+0)/2 ? Since the given info is already the boundaries, shouldn't we calculate midpoint from the boundaries?
Mark scheme: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s11_ms_63.pdf

Another example: http://freeexampapers.automaticpapers.com/as-a-level/mathematics-9709/9709_s14_qp_62.pdf
Q6(iii)
Mark scheme: http://freeexampapers.automaticpapers.com/as-a-level/mathematics-9709/9709_s14_ms_62.pdf

The ways to get midpoints for these two questions are different.. How come?

for 9709_s14_qp_62
Time (seconds) is a type of continuous data --> the values are representing class boundaries
for 9709_s11_qp_63
Mark is a type of discrete data --> you should write the intervals: <10 means until and including 9, < 20 means until and including 19 etc so the intervals are 0≤mark≤9, 10≤mark≤19 etc and the class boundaries are -0.5 to 9.5, 9.5 to 19.5 etc

 

[asadalam]

Guys wheres the MF9 page file for math formulae?i cant find it..

 

[Amy Bloom]

in statistics "A or B" means "A or B or both"
P(A or B)=P(A)+P(B)-P(A and B)
P(A given B) = P(A|B)= P(A and B)/P(B)
so P(D)=0.25, P(C)=0.4, P(C and D)=0.15
i) P(D or C)=0.25+0.4-0.15=0.5
ii) P(D or C but not both)=0.5-0.15=0.35
iii)P(D|C)=P(D and C)/P(C)=0.15/0.4=0.375
iv) P(C`|D)=0.1/0.25=0.4 as 25 have dogs and 15 have both --> 10 have a dog but don't have a cat, so P(C` and D)=10/100=0.1

Thank you Maleko

 

[RadzMau]

Hi. Can anyone help me with this S1 question please? Number 4(i)

 

[Syamsundar Menon]

Hey guys I need help with Mechanics A2 question. May/June 2011 51. I don't understand the marking scheme. Please send a picture of the worked out answer. Thank you

 

[mindy Min Yee]

hey guys I'm new here, just joined few days ago, Nice to meet all of you
Can i get a little help on Question 6 (iii)? I don't quite get the marking scheme I really am bad in P & C Someone help me!

 

[Thought blocker]

zAi NaB

 

[RoOkaYya G]

Guys wheres the MF9 page file for math formulae?i cant find it..

 

[abdul moeed rana]

wat does the phrase,"within 1 standard deviation of the mean" means????
please reply !!!have cie exam 2morrow

 

[abdul moeed rana]

google it!!

 

[abdul moeed rana]

zAi NaB

wat does the phrase,"within 1 standard deviation of the mean" means????
please reply !!!have cie exam 2morrow

 

[abdul moeed rana]

Hey everyone!
I have a question which is confusing me, can anyone answer that for me... explain me the steps to go thru.
In a group of 100 people, 40 own a cat, 25 own a dog and 15 own a cat and a dog. Find the probability that a person chosen at random:
(i) owns a dog or a cat [Answer: 0.5]
(ii) owns a dog or a cat but not both [Answer 0.35]
(iii) owns a dog given he owns a cat [Answer 0.375]
(iv) does not own a cat given that he owns a dog [Answer 0.4]
Thank you

wat does the phrase ,within 1 standard deviation of the mean means????

 

[abdul moeed rana]

hey guys I'm new here, just joined few days ago, Nice to meet all of you
Can i get a little help on Question 6 (iii)? I don't quite get the marking scheme I really am bad in P & C Someone help me!

wat does the phrase within 1 stadard deviation of the mean ....,means??