Mathematics: Post your doubts here!

[Aarjit]

Help please:

Find the number of different ways in which the 9 letters of the word GREENGAGE can be arranged if exactly two of the Gs are next to each other.
The answer is 5040.. but I'm confused because there's 3 Gs and I don't know how to find the # of ways where 2 Gs are separated from the other one.

Simply 'choose' 2 Gs out of 3, and the remaining 7 letters can be completely random!

G G _ _ _ _ _ _ _...............[consider GG to be 'attached' together so that it can alternate in 2! ways]

n = 2! x 3c2 x 7!.................. [but don't forget that there are 3 recurring Es too!]
..............3!
...= 5040...... Q.E.D

 

[kirashinagami]

Hai there. Can somebody help me to explain all the questions? http://www.xtremepapers.com/papers/...S Level/Mathematics (9709)/9709_s11_ms_72.pdf Just a brief explanation. I don't have a really good basic s2. So please help me! I am still trying to understand the concepts. Any tips in doing the questions will be greatly appreciated! Thank you..

 

[Aarjit]

Hai there. Can somebody help me to explain all the questions? http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s11_ms_72.pdf Just a brief explanation. I don't have a really good basic s2. So please help me! I am still trying to understand the concepts. Any tips in doing the questions will be greatly appreciated! Thank you..

I recommend you to go through the Examiner's Report: http://www.xtremepapers.com/papers/...d AS Level/Mathematics (9709)/9709_s11_er.pdf

Also, you can check out the KhanAcadamy Statistics' playlist for the core concepts: http://www.youtube.com/playlist?list=PL4C863861E3B2E380

 

[leosco1995]

Simply 'choose' 2 Gs out of 3, and the remaining 7 letters can be completely random!

G G _ _ _ _ _ _ _...............[consider GG to be 'attached' together so that it can alternate in 2! ways]

n = 2! x 3c2 x 7!.................. [but don't forget that there are 3 recurring Es too!]
..............3!
...= 5040...... Q.E.D

But there are also 3 Gs... so don't we have to divide by 3! twice?

 

[Aarjit]

But there are also 3 Gs... so don't we have to divide by 3! twice?

There is only 1 G that you can possibly alternate. The 2 Gs are fixed/'attached', so that they're always together.

The typical logic of dividing by 3! for the recurring 3Gs doesn't really serve well for this question. Albeit, there are various methods of doing it, I simply outlined mine.

Spend some time in it; you'll definitely get it.

 

[kirashinagami]

Ok thx for ur advices! I will ask you specific questions then... http://www.xtremepapers.com/papers/...S Level/Mathematics (9709)/9709_s11_qp_72.pdf how to solve no 2? I still don't understand how to find variance of a sample mean

 

[kirashinagami]

Please part 3
3
The number of goals scored per match by Everly Rovers is represented by the random variable X which has mean 1.8.
(i) State two conditions for X to be modelled by a Poisson distribution.
[2]
Assume now that X ∼ Po(1.8).
(ii) Find P(2 < X < 6).
[2]
(iii) The manager promises the team a bonus if they score at least 1 goal in each of the next 10 matches. Find the probability that they win the bonus. [3]

 

[leosco1995]

There is only 1 G that you can possibly alternate. The 2 Gs are fixed/'attached', so that they're always together.

The typical logic of dividing by 3! for the recurring 3Gs doesn't really serve well for this question. Albeit, there are various methods of doing it, I simply outlined mine.

Spend some time in it; you'll definitely get it.

I think I get it now. Basically, the 2 Gs are separated as a separate component so there isn't a need to use 3! for them. I think this was a pretty tricky question though. P&C sucks.

 

[Aarjit]

Please part 3

I can see that you're looking for help, but your paper 72 is on 29th May. We'll revise it after the 25th. Till then, post you queries in an S2 thread.
You might want to check out this too: http://www.examsolutions.co.uk/maths-revision/index.php#Statistics

 

[shan5674]

http://www.xtremepapers.com/papers/...S Level/Mathematics (9709)/9709_s11_qp_61.pdf

Q5 pleasee

 

[angelicsuccubus]

doesn't anyone here do mechanics 2?

cause I need notes/help anything!

 

[Wanzi21]

How do you do the part 3? permutation and combination question

 

[Zishi]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s11_qp_61.pdf

Q5 pleasee

Which part?

 

[Zishi]

View attachment 10386

How do you do the part 3? permutation and combination question

The best way to do questions of this type is to subtract the "No woman is included" from the total number of selections that can be made.

 

[shan5674]

Which part?

both :/

 

[Wanzi21]

The best way to do questions of this type is to subtract the "No woman is included" from the total number of selections that can be made.

then whats the total number? im so confused

 

[Zishi]

both :/

What is the formula for normal distribution?

then whats the total number? im so confused

Total number of selections is 9C3, 'cause you're selecting 3 people from 9 of them.

 

[DragonCub]

View attachment 10386

How do you do the part 3? permutation and combination question

(iii) To ensure at least one woman chosen, first step is to choose 1 from 3 women, which is 3C1.Then randomly choose the other 2 from the remaining 8 people. Overall it is 3C1 × 8C2 = 84

 

[Wanzi21]

(iii) To ensure at least one woman chosen, first step is to choose 1 from 3 women, which is 3C1.Then randomly choose the other 2 from the remaining 8 people. Overall it is 3C1 × 8C2 = 84

ohh yeap.. thank you.. gretly appreciated ^^

 

[ppaayas]

Care to explain please
3 A fair five-sided spinner has sides numbered 1, 2, 3, 4, 5. Raj spins the spinner and throws two fair
dice. He calculates his score as follows.
• If the spinner lands on an even-numbered side, Raj multiplies the two numbers showing on
the dice to get his score.
• If the spinner lands on an odd-numbered side, Raj adds the numbers showing on the dice to
get his score.
Given that Raj’s score is 12, find the probability that the spinner landed on an even-numbered side.