Mathematics: Post your doubts here!

[Khan_971]

5 The weights of letters posted by a certain business are normally distributed with mean 20 g. It is
found that the weights of 94% of the letters are within 12 g of the mean.
(i) Find the standard deviation of the weights of the letters. [3]

This is from Oct/Nov 2011, paper 61. I only have a doubt with how the question is phrased. It says 94% are WITHIN 12 g of the mean. So if we say that 94% of the weights lie between, per say, 26 g and 14 g, shouldn't that also be right? In the marking scheme they use 32 g. Shouldn't they stick to saying that 94% of the weights are below a value which is 12 g above the mean instead of writing within?
Thanks.

Lower boundary, 20-12 = 8, upper 20+12 = 32.
P( 8<X<32) =.94

 

[Khan_971]

no there will be more combinations... such as 20000 or above. 30000 and above and so on

then won't that go on??

 

[mukki]

can someone please explain how to solve question 6 (ii)
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s10_qp_63.pdf
it doesn't ever come as 4 and 2

u know that 0.028 = 0.85r -.82q
the possible values of r is 2 or 3 and for q 3 or 4. try each value for both and ul realize that r=4 and q=2 for the iqr to be 0.028

 

[Pals_1010]

no there will be more combinations... such as 20000 or above. 30000 and above and so on

You're right!

When you consider 5-digit numbers, No of integers = 5! = 120

Total no of integers = 72 + 120 = 192

Thanks

 

[Khan_971]

Pals_1010
I got it.

I got that as well but the answer in the book is 192

How is that possible?

if theres a 5 digit number. and without repetition. it will be 5! as all those 5 numbers can be either way. 5! + 72 = 192

 

[Pals_1010]

Pals_1010
I got it.
if theres a 5 digit number. and without repetition. it will be 5! as all those 5 numbers can be either way. 5! + 72 = 192

Thanks a lot . It clicked in my mind at the same time as yours it seems

 

[usmiunique]

I got that as well but the answer in the book is 192

How is that possible?

yes it can b either a 4 digit number or 5 digit numer..
for 4 digt numer u found out 72 possible ways. for 5 digit number, all numbers will be greater than 4000 so that is 5! numbers..
so, the total is 72+5!=192

 

[mukki]

i dont exactly understand the quartiles part.. what do u mean by deleting them from the list? :-S

i mean that circle the median and dont use it in your calculation its for un grouped data. look if the median is odd make a mark on each side of the median and calculate the MEDIAN for all the values before the median which will result as q1 and calculate the MEDIAN for all the values after the median which will result in q3. TRY IT OUT BUT PLZ DONT INCLUDE THE MEDIAN IF IT IS FROM AN ODD NUMBER.

 

[mominzahid]

3 diff colors:
Red,red,not red, not red = 2C2 * (5 * 2C1) x 4!/2! since 4 pegs and 2 are same
Since the rest 5 colors have 2 pegs each.
Total= (5*2C1) * 4!/2! * 6
= 720

i dont get itt.. :'(
i think i have problem in the basic concept of applying these factorials and permutations and combinations.. :/

 

[GoodRobot]

yes the cambridge s1 book by steve dobbs

found it.thanks xD

 

[azambezi]

In stats 1 when drawing the cumulative graph do u draw a curve or one with straight lines?

 

[Aarjit]

can you plz do part iii as well! thanks

[Q4] (iii) Find the number of different selections of 4 letters from the 9 letters of the word HAPPINESS which contain no Ps and either one or two Ss.

Discard all the Ps and keep the Ss aside:

H A P P I N E S S

H A I N E ........... S S

1st Criteria: 1S no Ps

S _ _ _ ......... [Note that you need to fill the 3 _ _ _ with the remaining 5 (the other S is discarded with P since we need only 1S) letters 'H A I N E' and S remains fixed; the order does not matter since we are 'selecting']

n = 1 x 5C3 = 10

2nd Criteria: 2S no Ps

S S _ _ ......... [Now there are merely 2 _ _ for the 5 letters 'H A I N E' and the 2 Ss remain fixed]

n'= 1 x 5C2 = 10.... [If you're wondering why I used '1 x' again instead of '2 x' or '2!' , it's because both the letters (S) are the same and it won't make a difference if we swap them. Again, the order does not matter since we are 'selecting']

∑ n = n + n' = 10 + 10 = 20...... Q.E.D.

 

[Khan_971]

In stats 1 when drawing the cumulative graph do u draw a curve or one with straight lines?

kind of sigmoid curve

 

[smartangel]

http://www.xtremepapers.com/papers/...S Level/Mathematics (9709)/9709_s11_qp_63.pdf
Q6

 

[usmiunique]

i mean that circle the median and dont use it in your calculation its for un grouped data. look if the median is odd make a mark on each side of the median and calculate the MEDIAN for all the values before the median which will result as q1 and calculate the MEDIAN for all the values after the median which will result in q3. TRY IT OUT BUT PLZ DONT INCLUDE THE MEDIAN IF IT IS FROM AN ODD NUMBER.

oh... thanks a lot!

 

[Khan_971]

i dont get itt.. :'(
i think i have problem in the basic concept of applying these factorials and permutations and combinations.. :/

Its gonna be tough writing here. I suggest khanacademy.org or your teacher

 

[hm12]

http://www.xtremepapers.com/papers/...AS Level/Mathematics (9709)/9709_w03_qp_6.pdf
please someone explain question 4 please

 

[leadingguy]

http://www.xtremepapers.com/papers/...S Level/Mathematics (9709)/9709_w09_qp_61.pdf
http://www.xtremepapers.com/papers/...S Level/Mathematics (9709)/9709_w09_ms_61.pdf

qstn 3 part i)

100 -100/7 = 0 so frm where this o.5 came????

 

[Esme]

Plz explain why the ans for (i) is 10C1+10C3+10C5+10C7+10C9. i knw they said 'odd numbr' of cups but whats the mathematical logic/reason behind it ??View attachment 10571

help me with this plzzz

 

[sea_princess]

u know that 0.028 = 0.85r -.82q
the possible values of r is 2 or 3 and for q 3 or 4. try each value for both and ul realize that r=4 and q=2 for the iqr to be 0.028

thanx , so it is just by trial, I mean we don't solve equations or anything?