Maths Question - Series 🥴

Screenshot 2019-10-21 at 12.08.53.png42.9KB

Just incase my layout of the question is not understandable.

Reply 2

Original post by badmathkid

Just incase my layout of the question is not understandable.

Wow that is an extremely badly worded question! Do you understand what they are asking or is that your question (I'm hoping that I know what they mean :smile:

)? If you understand it, please show us what you've tried.

(edited 4 years ago)

Reply 3

@RDKGames I assume they're basically asking for how many terms of the series you need to sum before reaching -50. Is that how you interpret it?

Reply 4

Original post by Sir Cumference

Wow that is an extremely badly worded question! Do you understand what they are asking or is that your question (I'm hoping that I know what they mean!)? If you understand it, please show us what you've tried.

That's what I thought. I don't think I understand the question anymore after I tried two different methods of this and ended up with a negative value of n.

I first tried finding the first term (a) and the common difference (d). I then used the arithmetic formula and subbed in -50 for the value of (Un) along with (a) and (d). This gave me an answer of -76/7.

I then tried using the arithmetic sum formula and used the same values for (a) and (d) as above but instead subbed (Sn) as -50. I got a weird quadratic which gave me both negative values of n. 🤯

Reply 5

Original post by badmathkid

For what value of n does the series fall short of -50?

(summation) 40 - 7n (n=1 to infinity)

Any help will be greatly appreciated! :smile:

this question is just completely wrong, I understand what its trying to ask but its just so wrong.
The n should be replaced with r and the infinity should be replaced with n.

Reply 6

RDKGames

Study Forum Helper

Original post by Sir Cumference

@RDKGames I assume they're basically asking for how many terms of the series you need to sum before reaching -50. Is that how you interpret it?

Whoever wrote this question needs to be arrested. Thats how I'd interpret it.

Obviously this is not a finite sum and has no convergence, so it must be asking for the number of terms needed to get the partial sum close to -50.

Reply 7

Phew, I thought I was the problem here. 😅

Reply 8

Original post by badmathkid

Phew, I thought I was the problem here. 😅

Where did you get the question from out of interest?

Reply 9

Original post by badmathkid

Phew, I thought I was the problem here. 😅

I've worked it out how the question should be asked, do you want the solution or do you want to try it out?

Reply 10

BrandonS15

Original post by RDKGames

Would the answer be 12 terms?

Reply 11

Original post by Sir Cumference

Where did you get the question from out of interest?

My lecturer for Mathematics apparently.

Reply 12

Original post by badmathkid

My lecturer for Mathematics apparently.

Uh oh that’s not a good sign :lol:

Reply 13

Original post by yankang.qi

I've worked it out how the question should be asked, do you want the solution or do you want to try it out?

Thank you for your help. Would you provide me with solution? I've been trying this for a while now and it's doing my head in. :colonhash:

Reply 14

Original post by Sir Cumference

Uh oh that’s not a good sign :lol:

Ikr!

Reply 15

Original post by badmathkid

Thank you for your help. Would you provide me with solution? I've been trying this for a while now and it's doing my head in. :colonhash:

no problem :smile:

Reply 16

Original post by yankang.qi

no problem :smile:

Wow this makes so much sense! Thanks a million! :five:

Reply 17

Original post by badmathkid

Wow this makes so much sense! Thanks a million! :five:

No problemo :smile:

Reply 18

BrandonS15

Original post by yankang.qi

no problem :smile:

n=12 comes closer to -50 than n=11 at n=11 you get -22 total at n=12 you get -66 total. -66 is closer to -50 than -22 so wouldn’t n=12 be the answer?
It says “fall short of” so wouldn’t it want an answer thats smaller than -50 and closest which would be -66 when n=12

(edited 4 years ago)

Reply 19