Mathematics: Post your doubts here!

[The Sarcastic Retard]

I haven't studied the other topics. So may be someone else might help.

Thanks...

 

[Jennifer4678]

Hey!! Can someone please help me with this question. It is not a past year paper though


and another one

am i supposed to find the 'average velocity', how do i identify what t is?

Thanks so much!! any help would be much appreciated

 

[nehaoscar]

Hey!! Can someone please help me with this question. It is not a past year paper though
View attachment 59085
Thanks so much!! any help would be much appreciated

Idk if this is correct?
Using s = ut + 0.5at^2

 

[nehaoscar]

Ok so when a variable is added the new mean is [E(x-a)/n] + a (assume E means summation sign )
So then I had read in the text book that the mean changes on adding any variable but the standard deviation is unchanged
So if the mean changes, how can we still equate them both together??

 

[Eugene99]

View attachment 59090
View attachment 59092
Ok so when a variable is added the new mean is [E(x-a)/n] + a (assume E means summation sign )
So then I had read in the text book that the mean changes on adding any variable but the standard deviation is unchanged
So if the mean changes, how can we still equate them both together??

They equated the mean after adding 100 which balanced the 100 which was subtracted earlier

 

[nehaoscar]

Part iv
So I got 9/16 and 13/16 but then the answer comes out as 9/13 .... does 0 not count as positive?? But on the RHS in the mark scheme they accept those fractions which include the zero ... so will 9/13 be right or no??

 

[Rizwan Javed]

View attachment 59093

View attachment 59094
Part iv
So I got 9/16 and 13/16 but then the answer comes out as 9/13 .... does 0 not count as positive?? But on the RHS in the mark scheme they accept those fractions which include the zero ... so will 9/13 be right or no??

I don't think so it'll be right. Actually 0 is neither counted as positive nor negative. So if you'll exclude zero, which you might have included, I think you'll get the right answer.

 

[nehaoscar]

I don't think so it'll be right. Actually 0 is neither counted as positive nor negative. So if you'll exclude zero, which you might have included, I think you'll get the right answer.

Yep excluding 0 givers the right answer but since the ms says accept any of the fractions which includes the 9/13 i think they'll give 1 mark right?

 

[Rizwan Javed]

Yep excluding 0 givers the right answer but since the ms says accept any of the fractions which includes the 9/13 i think they'll give 1 mark right?

Yes, you'll get only the Method Mark (M1). But not the answer mark since your answer is wrong.

 

[Konstantino Nikolas]

http://papers.gceguide.com/A Levels/Mathematics (9709)/9709_w14_qp_43.pdf
6.(iii) Shouldn't the greatest height be => 0.5*1.4*4 = 2.8 ?? Why does the ms say 4.8?

 

[Rizwan Javed]

http://papers.gceguide.com/A Levels/Mathematics (9709)/9709_w14_qp_43.pdf
6.(iii) Shouldn't the greatest height be => 0.5*1.4*4 = 2.8 ?? Why does the ms say 4.8?

You also have to add the value of 'h' to this which is 2 as the question says you to find the Maximum height above the FLOOR.

So the maximum height reached will be

0.5*1.4*4 +2 = 4.8

 

[Konstantino Nikolas]

You also have to add the value of 'h' to this which is 2 as the question says you to find the Maximum height above the FLOOR.

So the maximum height reached will be

0.5*1.4*4 +2 = 4.8

Oh right yeah ok thanks

 

[i_try9621]

For 5) i) , in the markscheme the highlighted part is my doubt. Shouldn't it be just "h" ?

 

[Konstantino Nikolas]

View attachment 59113 For 5) i) , in the markscheme View attachment 59115 the highlighted part is my doubt. Shouldn't it be just "h" ?

The two similar triangles taken are the shaded ones. So the 12 cm side of the blue one corresponds to (12 - h) cm of the red one.

If you take it as (h) cm, then the relation would be: 6/12 = (6-r)/h

 

[nehaoscar]

W13-62


S13-61



Ok so I know how to solve these questions but then I want to know why different methods are used and why the other method doesn't give the correct answer?
Like in the letter one they have done total possible combinations - if the vowels were together
Now if I apply this same logic to the second question of the families I get a different answer :/
like : total combination = 14!
all adults are together = 6! * 9!
so then 14! - (6!*9!) doesn't give the right answer...
why not??
Even with the top one if i use the method used in the second question doing [(7!/2!2!)*(8P4/3!)] also gives the wrong answer :/
Anum96 Rizwan Javed

 

[Rizwan Javed]

W13-62
View attachment 59125
View attachment 59126
S13-61
View attachment 59122
View attachment 59123

Ok so I know how to solve these questions but then I want to know why different methods are used and why the other method doesn't give the correct answer?
Like in the letter one they have done total possible combinations - if the vowels were together
Now if I apply this same logic to the second question of the families I get a different answer :/
like : total combination = 14!
all adults are together = 6! * 9!
so then 14! - (6!*9!) doesn't give the right answer...
why not??
Even with the top one if i use the method used in the second question doing [(7!/2!2!)*(8P4/3!)] also gives the wrong answer :/
Anum96 Rizwan Javed

Actually you're missing some of the possible orders. You calculated that all the adults go together. But it is also possible that only 2 adults go together, and the rest do not and so on. So infact you're missing some of the possible orders.

Consider that all the adults are represented by * and children by 'x'. In order to have no 2 adults together, there must be atleast 1 children in between any two adults.

* x * x * x * x * x * x * x * x *

^ Let this represent the possible positions the adults or children can take.

There are 6 adults, so you've to select 6 ' * 's from the nine shown above where adults are to be placed.

9C6 * 6! <--- The number of different ways in which this can be done.

Now arrange the 8 children in the possible 8 arrangements shown by 'x' s. This would be 8!.

Now combine them to find the total possible orders:

9C6 * 6! * 8! = 2438553600

I hope you understood.

 

[nehaoscar]

Actually you're missing some of the possible orders. You calculated that all the adults go together. But it is also possible that only 2 adults go together, and the rest do not and so on. So infact you're missing some of the possible orders.

Consider that all the adults are represented by * and children by 'x'. In order to have no 2 adults together, there must be atleast 1 children in between any two adults.

* x * x * x * x * x * x * x * x *

^ Let this represent the possible positions the adults or children can take.

There are 6 adults, so you've to select 6 ' * 's from the nine shown above where adults are to be placed.

9C6 * 6! <--- The number of different ways in which this can be done.

Now arrange the 8 children in the possible 8 arrangements shown by 'x' s. This would be 8!.

Now combine them to find the total possible orders:

9C6 * 6! * 8! = 2438553600

I hope you understood.

Oh ok yes I see! I didn't realize that there would be different orders with not all but some of the adults together
Thanks a lot!

 

[holoholo]

Can some please show me the sketch and shading of this ?

 

[nehaoscar]

Can some please show me the sketch and shading of this ?

View attachment 59129

 

[nehaoscar]

S14-31
Pls explain part ii