I'm an IGCSE Maths Teacher - Post your questions here.

[Ahmed Nasser]

i want to know if theres any formulas for the nth term like the a+(n-1)d ??? because i'm really losing too much from the nth term question

 

[notnek01]

You need to explain how a cumulative frequency graph is plotted. Remember, the value on the x-axis is the endpoint of the interval and the value on the y=axis is the cumulative frequency.

So for the interval, 50<=m<60, the endpoint is 60 and the cumulative frequency is 20+60+200=280.

You would get 1 mark for saying that the endpoint is 60 and 1 mark for writing 20+60+200=280.

 

[Noorullah Farid]

i want to know if theres any formulas for the nth term like the a+(n-1)d ??? because i'm really losing too much from the nth term question

yeah this is the formula here "a" is the 1st term and "d" is the difference between 2 consecutive terms of the sequence..
note: only works for sequences with common difference

 

[notnek01]

wow I never knew this,thank you so so much!!!
if they say Pablo plants x lemon trees and y orange trees.
(a) (i) He plants at least 4 lemon trees.
Write down an inequality in x to show this information
why cant we write x >= 4 as they are saying ATLEAST which means equal or greater than right?the answer was x>4 without the equal to sign..

Which paper did you get this question from? The answer should be x>=4.

 

[Noorullah Farid]

You need to explain how a cumulative frequency graph is plotted. Remember, the value on the x-axis is the endpoint of the interval and the value on the y=axis is the cumulative frequency.

So for the interval, 50<=m<60, the endpoint is 60 and the cumulative frequency is 20+60+200=280.

You would get 1 mark for saying that the endpoint is 60 and 1 mark for writing 20+60+200=280.

you mean from the table? i thought they were asking why the line is a curve.. thanks for the response

 

[Ebby_SaLeem]

If CIE paid me, I'd make mark schemes with explanations for every paper

HAHAHAHA!
ALRIGHT!!!

 

[inquisitiveness]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Mathematics (0580)/0580_s12_qp_42.pdf
q.3
and the mark scheme is here http://papers.xtremepapers.com/CIE/...s (with coursework) (0581)/0581_s12_ms_42.pdf

 

[notnek01]

i want to know if theres any formulas for the nth term like the a+(n-1)d ??? because i'm really losing too much from the nth term question

This has been asked a few times so I'll write a full answer:

For quadratic sequences (where the second difference is constant), you could use the formula: nth term = a+(n-1)d+0.5(n-1)(n-2)c where a is the first term, d is the difference between the first two terms and c is the second difference which is constant:

e.g. 3, 5, 8, 12, 17, ...

a=3 and the difference between 5 and 3 is 2 so d=2.

The first differences are 2, 3, 4, 5, ... so the second difference is 1 which is constant (this means it's a quadratic sequence). So c=1.

So the nth term is a 3 + 2(n-1) + 0.5(n-1)(n-2).

And you can simplify this to get the answer.


I don't really like teaching the formula, 1) It could be tricky to simplify the algebra and 2) You may get too used to using it and forget methods of substitution which are commonly asked at IGCSE.

For quadratic sequences (like the one above), I recommend the method in the final post on this page: https://www.xtremepapers.com/community/threads/mathematics-post-your-doubts-here.2565/page-162

 

[ZaqZainab]

fg(x) = f(g(x)) = f(1/x) = 1 - 2(1/x)

= 1 - 2/x = x/x - 2/x = (x-2)/x

Should it not be 1-2/2x??
when we multiply 2(1/x) the answer is 2/2x Yes?
I am kinda confused as it is brackets

 

[ZaqZainab]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Mathematics (0580)/0580_s12_qp_43.pdf question 9 d this questions are new to me
what i do is use the formula from the question and get the answer E,B and A and this are WRONG

 

[inquisitiveness]

should sequences always be in this bracket form or can they be expanded cause in this answer it says n(n +1) π oe final answer
SC1 for a quadratic expression
e.g.n2 + n π
SC1,meaning they would give us only one mark
I know how to find the sequence i just want to know the format it should be written in like in bracket or expanded
im talking about this Q if you need this infomation,http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Mathematics (0580)/0580_s12_ms_43.pdf q.11 d

 

[notnek01]

Should it not be 1-2/2x??
when we multiply 2(1/x) the answer is 2/2x Yes?
I am kinda confused as it is brackets

No, if you multiply a fraction by a number, you only multiply the numerator by that number.

E.g. (1/2) * 3 = 3/2

Using your method, (1/2) * 3 = 3/6 which is wrong.

 

[inquisitiveness]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Mathematics (0580)/0580_s12_qp_43.pdf question 9 d this questions are new to me
what i do is use the formula from the question and get the answer E,B and A and this are WRONG

you kind of have eto know the shapes for these,stright line,cubic,1/something graphs...

 

[aaaamfa]

need help in the following question:
0580/41/m/j/10
question no. 2b

plzz ans

 

[notnek01]

you mean from the table? i thought they were asking why the line is a curve.. thanks for the response

I'm not sure why you thought that - the question didn't mention anything about a curve.

The curve has been drawn using the table so you need to use the info. in the table to answer the question.

 

[notnek01]

plzz ans

I already answered this in post #208.

 

[notnek01]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Mathematics (0580)/0580_s12_qp_42.pdf
q.3
and the mark scheme is here http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Mathematics (with coursework) (0581)/0581_s12_ms_42.pdf

I'm not going to do the whole question for you. Which part can't you do?

 

[inquisitiveness]

oh no i was not asking for the whole question,it was that inequality thing x >4,and i wrote x>=4,you wanted to know which year the question came from so i posted the year and the ms for q3 b,

 

[inquisitiveness]

sorry 3 a***

 

[notnek01]

oh no i was not asking for the whole question,it was that inequality thing x >4,and i wrote x>=4,you wanted to know which year the question came from so i posted the year and the ms for q3 b,

Sorry, there's a lot of questions on here and I'm trying my best to keep up!

There's a mistake in the marks scheme. All < and > should be <= and >=. The examiners report for that year contains the correct answers.