Guys, are you sure the Sequence Question was CORRECT in Math

[Rashu712]

This was the question about Sequence in Paper 4 and a friend of mine who used to be a math teacher says that the question is WRONG.

Because if you solve for the first 2 or 3 diagrams, a and b's value only satisfies the conditions for maximum 3rd diagram. From 4th diagram and onwards, the results are wrong.

We had to find the number of 1 cm lines using their formula:

an^3 + bn^2 + n

Can you try to solve it for me here again and then check if your values for a and b work for n diagrams? (4,5 and so on)

 

[Rashu712]

Re: Guys, are you sure the Sequence Question was CORRECT in

Please respond.

 

[Adahshan]

Re: Guys, are you sure the Sequence Question was CORRECT in

Why people are argueing is because of these facts:

Simulatinious equations are tricky, If you start incorrectly, you will end correctly because if the first number is wrong then when diving and multiplying and replacing to get the second, it will be right but not really.

The true answer was 0.5 and 1.5

 

[seemo1995]

Re: Guys, are you sure the Sequence Question was CORRECT in

a=0.5
b=1.5

 

[Rashu712]

Re: Guys, are you sure the Sequence Question was CORRECT in

a=0.5
b=1.5

Why people are argueing is because of these facts:

Simulatinious equations are tricky, If you start incorrectly, you will end correctly because if the first number is wrong then when diving and multiplying and replacing to get the second, it will be right but not really.

The true answer was 0.5 and 1.5

If that's correct,

Then:

(0.5)n^3 + (1.5)n^2 + n = number of lines for nth diagram.

So we'll solve for Diagram 4.

(o.5) x 4^3 + (1.5) x 4^2 + 4 = number of lines.

(0.5) x 64 + (1.5) x 16 + 4 = number of lines.

32 + 24 + 4 = number of lines.

60 = number of lines for 4th Diagram.

Now count the number of lines for the 4th diagram and check if it's 60.

I counted and I get 30.

 

[Adahshan]

Re: Guys, are you sure the Sequence Question was CORRECT in

No offence to the above post but it's full of stupidity.

THE QUESTION WAS TOTAL NUMBER OF LINES, NOT DIAGRAM 4.

You must count total, it wasn't for per diagram, you forgot the question. it was for the total number of lines.

 

[Adahshan]

Re: Guys, are you sure the Sequence Question was CORRECT in

If your right about 30, then 1st has 3, second has 9, and third 18.. so 60 = total number. WORKED

 

[Rashu712]

Re: Guys, are you sure the Sequence Question was CORRECT in

No offence to the above post but it's full of stupidity.

THE QUESTION WAS TOTAL NUMBER OF LINES, NOT DIAGRAM 4.

You must count total, it wasn't for per diagram, you forgot the question. it was for the total number of lines.

It was for n diagrams. I didn;t forget, I discussed with my classmates. They said it;s total number of lines for for nth diagrams.

 

[Adahshan]

Re: Guys, are you sure the Sequence Question was CORRECT in

No, Your mistaken.

Total number for nth diagrams yes and you chose 4 as n so total is 60, Dude i had teachers do this question and discuss it, I don't think you can prove any point.

 

[veteran]

Re: Guys, are you sure the Sequence Question was CORRECT in

it was for the total number of lines in the all the first n diagrams

 

[Dooouuu]

Re: Guys, are you sure the Sequence Question was CORRECT in

@Adahshan : I totally agree with

 

[Divalicious]

Re: Guys, are you sure the Sequence Question was CORRECT in

OMG guys...
n is not the diagram number. The question said 'FOR THE FIRST N DIAGRAMS'
That means when you take 'n' as 2, it's equal to the sum of lines in the FIRST TWO DIAGRAMS = 12 NOT 9
Same thing with 'n' as 3, 'FIRST THREE DIAGRAMS' = 3+9+18= 30 NOT 18
I hope you get it. And try it yourself till like n=4 or n=5, and always add all the diagrams before, you'll always see it's right

 

[starr542]

Re: Guys, are you sure the Sequence Question was CORRECT in

U think they'll cut all marks, if ur formula is right bt ur answer is wrong?

 

[IGCSEdude]

Re: Guys, are you sure the Sequence Question was CORRECT in

@rashu... The equation doesn't apply for one diagram individually ( except for the first one ) , but it applies for the total number of the lines in the first n diagrams. That is, (0.5x2^3)+(1.5x2^2)+2=number of 1cm lines in diagram 1 + number of 1cm lines in diagram 2

 

[najjar10]

Re: Guys, are you sure the Sequence Question was CORRECT in

I'm glad we had that question as our sequence question. It was relatively easy compared with other exams.
It's weird that we had no Venn Diagrams, %'s and ratios, and very little probability.

 

[SmartNour]

Re: Guys, are you sure the Sequence Question was CORRECT in

then how come i got -0.25 and 2.25
even mi friends got the same answerrr

 

[starr542]

Re: Guys, are you sure the Sequence Question was CORRECT in

then how come i got -0.25 and 2.25
even mi friends got the same answerrr

I got the same answer too. and most of my friends did too.

 

[imanmalik]

Re: Guys, are you sure the Sequence Question was CORRECT in

HAHAI GOT IT RIGHT!

 

[burndtjamb]

Re: Guys, are you sure the Sequence Question was CORRECT in

I'm glad we had that question as our sequence question. It was relatively easy compared with other exams.
It's weird that we had no Venn Diagrams, %'s and ratios, and very little probability.

Wow I never realised that! I'm SO glad they didn't have any questions on sets, I hate that topic so much! :Yahoo!: