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 Post subject: Maths sequence helpPosted: Tue Jun 28, 2016 11:24 pm

Joined: Tue Dec 01, 2015 12:54 pm
Posts: 4
Can anyone please tell me what the pattern is in this sequence please?

1, 1.5, 2.5, 4..... (Where I have put .5 it is actually written in the question as a fraction ie one and a half).

Apparently the next two numbers are 15 and a half and then 23 and a half (I looked at the answers!)

I want to explain why to my son but I can't see the pattern.

Many thanks in advance for any explanations.

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 Post subject: Re: Maths sequence helpPosted: Tue Jun 28, 2016 11:38 pm

Joined: Fri Jan 31, 2014 12:45 pm
Posts: 154
Are the answers def right? Otherwise adding the previous 2 numbers together would work. Or +0.5, +1, +1.5 etc.

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 Post subject: Re: Maths sequence helpPosted: Tue Jun 28, 2016 11:47 pm

Joined: Sat Jul 24, 2010 9:45 pm
Posts: 1488
I can't see how 15.5 and 23.5 can be the next two numbers, either - where does the question come from?

This sequence could also be based on a difference between the numbers increasing by 0.5 each time, i.e.:

1 (+0.5), 1.5 (+1.0), 2.5 (+1.5), 4 (+2.0), 6 (+2.5), 8.5

in which case the next two numbers would be 6 and 8.5.

I'm very curious to see how to get to the answer suggested in the book!

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It felt like I hit rock bottom; suddenly, there was knocking from beneath... (anon.)

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 Post subject: Re: Maths sequence helpPosted: Wed Jun 29, 2016 6:25 am

Joined: Sun Dec 20, 2015 5:24 pm
Posts: 186
Looks like a typo to me. Even if the question was what are the 7/8 th or 8th/9th terms rather than the "next one", adding the two previous numbers together gives 15 and 19, and adding 0.5 more each time gives 16.5 and 26.5.

I vote for "poor question"...

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 Post subject: Re: Maths sequence helpPosted: Wed Jun 29, 2016 6:50 am

Joined: Tue Dec 01, 2015 12:54 pm
Posts: 4
I'm glad you all think this is wrong too! I was up so late last night trying to work it out.

It is taken from Bond Maths Assessment Papers Book 1, 10-11+ years.

I think I'll give up! Thanks for your help all the same.

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 Post subject: Re: Maths sequence helpPosted: Wed Jun 29, 2016 10:53 am

Joined: Sat Jul 24, 2010 9:45 pm
Posts: 1488
Whirlwind wrote:
It is taken from Bond Maths Assessment Papers Book 1, 10-11+ years.

The answer in the book must be a print error.

I have found this question in Maths Assessment Book 1, 10-11+, published 2014 - paper 12, q. 36-37.

In the same book published in 2007, paper 12, q. 36-37 the sequence is different, namely: 8, 8 1/2, 9 1/2, 11 1/2.

I have both sets of answers and in one of them the answer is given as 6 and 8 1/2 and the other one shows the answer as 15 1/5 and 23 1/5.

The odd thing is, that either I swapped the answer sections between the books or there was error somewhere in the BOND's bank of questions/answers and in both books incorrect answers were printed for this particular question (i.e. questions and answers got swapped by mistake).

15 1/2 and 23 1/2 are answers to the sequence 8, 8 1/2, 9 1/2, 11 1/2 (the differences between the terms are doubling, i.e. 8 plus 1/2, plus 1, plus 2, plus 4, plus 8 etc.)

The answers to the sequence 1, 1 1/2, 2 1/2, 4 are 6 and 8 1/2 ( the differences between the terms are 1/2, 1, 1 1/2, 2 etc).

_________________
It felt like I hit rock bottom; suddenly, there was knocking from beneath... (anon.)

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 Post subject: Re: Maths sequence helpPosted: Wed Jun 29, 2016 12:13 pm

Joined: Tue Dec 01, 2015 12:54 pm
Posts: 4
Thanks Purpleduck.

Always a relief to know I'm not going mad, although what a wasted evening I had last night trying to figure it out!! Will mark the paper out of 48.

Thanks again.

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 Post subject: Re: Maths sequence helpPosted: Wed Jun 29, 2016 12:19 pm

Joined: Sat Jul 24, 2010 9:45 pm
Posts: 1488
Whirlwind wrote:
Thanks Purpleduck.

Always a relief to know I'm not going mad, although what a wasted evening I had last night trying to figure it out!! Will mark the paper out of 48.

Thanks again.
You're welcome. You're not going mad, Whirwind, although I do know what you mean...

_________________
It felt like I hit rock bottom; suddenly, there was knocking from beneath... (anon.)

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