The Student Room Group

Need help on c2 question arithmetic

ImageUploadedByStudent Room1460658688.048092.jpg
I only need help on C
I did the first part so I attached that as well
ImageUploadedByStudent Room1460658724.720385.jpg
I don't understand that question at all, so If you could explain, how to do it then it would be very helpful, thank you


Posted from TSR Mobile

Scroll to see replies

Original post by am99
ImageUploadedByStudent Room1460658688.048092.jpg
I only need help on C
I did the first part so I attached that as well
ImageUploadedByStudent Room1460658724.720385.jpg
I don't understand that question at all, so If you could explain, how to do it then it would be very helpful, thank you


Posted from TSR Mobile


The sum of the first 25 terms is given to you in the question so you can substitute that into the equation. If you then substitute x as the sum of the first k numbers, you get the equation 33(3500-x)=67x which you can then solve. Hope that helps :smile:
Reply 2
Original post by LilacFlorence
The sum of the first 25 terms is given to you in the question so you can substitute that into the equation. If you then substitute x as the sum of the first k numbers, you get the equation 33(3500-x)=67x which you can then solve. Hope that helps :smile:


Ok I understand thank you for your help !


Posted from TSR Mobile
Reply 3
Original post by LilacFlorence
The sum of the first 25 terms is given to you in the question so you can substitute that into the equation. If you then substitute x as the sum of the first k numbers, you get the equation 33(3500-x)=67x which you can then solve. Hope that helps :smile:


ImageUploadedByStudent Room1460788455.191815.jpg
Could you help me on that question,
You don't have to do it just show me so I can start it, both part of the question


Posted from TSR Mobile
Original post by am99
ImageUploadedByStudent Room1460788455.191815.jpg
Could you help me on that question,
You don't have to do it just show me so I can start it, both part of the question


Posted from TSR Mobile


Question 6bi and ii or 7a and b?
Reply 5
Original post by LilacFlorence
Question 6bi and ii or 7a and b?


Question 6bi and ii


Posted from TSR Mobile
Original post by am99
Question 6bi and ii


Posted from TSR Mobile


Ok so for the first part you need to put the numbers you've been given into the equation Un = a + (n ā€“ 1)d.
Then for part ii) you know that Uk = 0 so you can replace Un with 0, and n with k in the equation you found in part i) so that you can find what k equals. Then you can use this value in the Sn = 1/2 n(a + l) equation.
Let me know if you'd like some more hints :smile:
Reply 7
Original post by LilacFlorence
Ok so for the first part you need to put the numbers you've been given into the equation Un = a + (n ā€“ 1)d.
Then for part ii) you know that Uk = 0 so you can replace Un with 0, and n with k in the equation you found in part i) so that you can find what k equals. Then you can use this value in the Sn = 1/2 n(a + l) equation.
Let me know if you'd like some more hints :smile:


Okay thanks, I will reply soon after I do


Posted from TSR Mobile
Reply 8
Original post by LilacFlorence
Ok so for the first part you need to put the numbers you've been given into the equation Un = a + (n ā€“ 1)d.
Then for part ii) you know that Uk = 0 so you can replace Un with 0, and n with k in the equation you found in part i) so that you can find what k equals. Then you can use this value in the Sn = 1/2 n(a + l) equation.
Let me know if you'd like some more hints :smile:


ImageUploadedByStudent Room1460833471.078565.jpg
Is this right so far? Afterward I am confused as to what to put in the equation, I use this one instead
1/2n(2a+(n-1)d
So 1/2n(2(240)+(n-1)d
But what is N, is it the k value or n=1?


Posted from TSR Mobile
Original post by am99
ImageUploadedByStudent Room1460833471.078565.jpg
Is this right so far? Afterward I am confused as to what to put in the equation, I use this one instead
1/2n(2a+(n-1)d
So 1/2n(2(240)+(n-1)d
But what is N, is it the k value or n=1?


Posted from TSR Mobile


Yes that is right :smile: n is the k value
Reply 10
Original post by LilacFlorence
Yes that is right :smile: n is the k value

okay, i just checked and i got the answer right, thank you for your help sorry if i bothered you
Original post by am99
okay, i just checked and i got the answer right, thank you for your help sorry if i bothered you


No problem at all - let me know if there's anything else I can help with :smile:
Reply 12
Original post by LilacFlorence
The sum of the first 25 terms is given to you in the question so you can substitute that into the equation. If you then substitute x as the sum of the first k numbers, you get the equation 33(3500-x)=67x which you can then solve. Hope that helps :smile:


Sorry to bother you but how do you do part a?
Original post by SANTR
Sorry to bother you but how do you do part a?


You need to use the formula Un = a+(n-1)d and sub in the values you have been given :smile:
Reply 14
Original post by LilacFlorence
You need to use the formula Un = a+(n-1)d and sub in the values you have been given :smile:


Oh right, I was confused because the title states 'C2' and arithmetic series isn't a C2 topic for Edexcel.
Original post by SANTR
Oh right, I was confused because the title states 'C2' and arithmetic series isn't a C2 topic for Edexcel.


yeah that confused me too -I think it's C2 for AQA :tongue:
Reply 16
Original post by LilacFlorence
No problem at all - let me know if there's anything else I can help with :smile:


ImageUploadedByStudent Room1461182544.259845.jpg
Could you help me on part a, I know it's a simultaneous equation but I just can't set up the equation, i find it so confusing


Posted from TSR Mobile
Original post by am99
ImageUploadedByStudent Room1461182544.259845.jpg
Could you help me on part a, I know it's a simultaneous equation but I just can't set up the equation, i find it so confusing


Posted from TSR Mobile


So using the equation you were given, you can form the equation 132 = 160p +q.
Then if you know the limit is 20 as it tends to infinity you can sub 20 into the equation L = pL + q to get 20 =20p + q and then solve the two equations simultaneously.
On the exam board I do we don't learn about limits - I just looked up about them quickly but sorry I can't really explain the limits bit any more than that! :tongue:
Reply 18
Original post by LilacFlorence
So using the equation you were given, you can form the equation 132 = 160p +q.
Then if you know the limit is 20 as it tends to infinity you can sub 20 into the equation L = pL + q to get 20 =20p + q and then solve the two equations simultaneously.
On the exam board I do we don't learn about limits - I just looked up about them quickly but sorry I can't really explain the limits bit any more than that! :tongue:

Ok thank you, sorry for the late Reply, I forgot about it completely ImageUploadedByStudent Room1461783049.651392.jpg
Could you help me on part C please.


Posted from TSR Mobile
Original post by am99
Ok thank you, sorry for the late Reply, I forgot about it completely ImageUploadedByStudent Room1461783049.651392.jpg
Could you help me on part C please.


Posted from TSR Mobile


You need to use the equation Sn =1/2n[2a+(nāˆ’1)d]
You know from part a and b that a=87 and d=-3 and you are told that n=k and Sn=0 so sub these numbers in and solve to find k :smile:

Quick Reply