C1 - finding number of terms in a sequence question

AlphaMolecule

4

removed

(edited 9 years ago)

Reply 1

TenOfThem

18

Original post by AlphaNick

I know how to do this and it can involve using the quadratic formula, but some of the examples I've come across in my textbook seem difficult to work out in your head

for example on page 105 in the Edexcel textbook the example ends with $n=\frac{-3\pm \sqrt{9+80000}}{10}$ and n being 27.9, rounding to 28 terms

are they going to expect us to do that without a calculator?

C1 is now a non-calculator paper

It was not always thus - hence some questions in text books are not non-calculator

Reply 2

blackened_sky

12

I'd definitely just leave that as -3+/-sqrt80009 / 10? There's no way you could work it out in your head

Reply 3

BabyMaths

It's not difficult to estimate

\dfrac{\sqrt{80009}}{10} \approx \sqrt{800}=20\sqrt{2}\approx 28.28

Reply 4

Aph

22

That last number is so big I'd ignore the 9 and estimate it at 200*root2 (aproximated to 1.45) inside the root which would be ok I think

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(edited 9 years ago)

Reply 5

Aph

22

Original post by AlphaNick

I could give a lot less straight forward example I encountered in the exercises where estimating isn't easy at all, I'm just clarifying whether or not they'll give you something like this and as I understand it TenOfThem said they have calculator questions because it wasn't always non-calculator. I'm not having a problem estimating, I'm was just hoping that someone could tell me whether or not they'll give questions like this.

Yeah I had some questions I needed to estimate in june thod year

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Reply 6

BabyMaths

Original post by AlphaNick

I could give a lot less straight forward example I encountered in the exercises where estimating isn't easy at all, I'm just clarifying whether or not they'll give you something like this and as I understand it TenOfThem said they have calculator questions because it wasn't always non-calculator.

Whilst TenOfThem's explanation is no doubt correct, there are calculations required (or avoidable) in C1 exams that some students consider to be unreasonable without a calculator.

Perhaps people rely too much on their calculators?

Reply 7

TheNicholas

2

Sequences is part of the C2 sillibus not C1 isn't it? Therefore you will have a calculator if I am not mistaken

Reply 8

TenOfThem

18

Original post by AlphaNick

I could give a lot less straight forward example I encountered in the exercises where estimating isn't easy at all, I'm just clarifying whether or not they'll give you something like this and as I understand it TenOfThem said they have calculator questions because it wasn't always non-calculator. I'm not having a problem estimating, I'm was just hoping that someone could tell me whether or not they'll give questions like this.

Original post by Aph

Yeah I had some questions I needed to estimate in june thod year

Just to clarify, as I am not sure what Aph is saying

There were no questions on Edexcel C1 June 14 that required you to estimate - all values could be found without a calculator

Reply 9

TenOfThem

18

Original post by TheNicholas

Sequences is part of the C2 sillibus not C1 isn't it? Therefore you will have a calculator if I am not mistaken

In Edexcel C1 has Arithmetic Series and C2 has Geometric Series

Reply 10

TenOfThem

18

Original post by BabyMaths

Whilst TenOfThem's explanation is no doubt correct, there are calculations required (or avoidable) in C1 exams that some students consider to be unreasonable without a calculator.

Perhaps people rely too much on their calculators?

Not the example given in the OP though :smile:

Reply 11

Aph

22

Original post by TenOfThem

Just to clarify, as I am not sure what Aph is saying

There were no questions on Edexcel C1 June 14 that required you to estimate - all values could be found without a calculator