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 Post subject: HELPPosted: Fri Aug 30, 2013 5:14 pm

Joined: Fri Mar 22, 2013 8:29 pm
Posts: 38
Hi

... Find the number that continues the series...

1 1 2 6 ?

120 95 79 70 ?

Which is the next number in each series and why?

Thank you

Erin

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 Post subject: Re: HELPPosted: Fri Aug 30, 2013 5:55 pm

Joined: Wed Nov 23, 2011 12:52 pm
Posts: 609
Location: Shamballa
First one is 24

1*1=1

1*2=2

2*3=6

6*4=24

Next one: series is -25,-17,-9 so next one is -1: answer is 69 (series increases by +8)

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"To err is human;to forgive ,divine"

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 Post subject: Re: HELPPosted: Fri Aug 30, 2013 6:02 pm

Joined: Fri Mar 22, 2013 8:29 pm
Posts: 38
Thank you

Erin

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 Post subject: Re: HELPPosted: Fri Aug 30, 2013 6:04 pm

Joined: Wed Jan 11, 2006 7:10 pm
Posts: 8764
Location: Buckinghamshire
Perfectly correct on the first one, IMT, but I'm afraid there's an error on the second.

120 - 25 = 95
95 - 16 = 79
79 - 9 = 70
70 - 4 = 66
... decreasing by square numbers.

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 Post subject: Re: HELPPosted: Fri Aug 30, 2013 6:14 pm

Joined: Wed Nov 23, 2011 12:52 pm
Posts: 609
Location: Shamballa
good spot

_________________
"To err is human;to forgive ,divine"

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 Post subject: Re: HELPPosted: Fri Aug 30, 2013 8:58 pm

Joined: Tue Jul 21, 2009 9:56 pm
Posts: 8545
Could the first one have another answer of 6 x 7 as well?

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 Post subject: Re: HELPPosted: Fri Aug 30, 2013 9:06 pm

Joined: Wed Jan 11, 2006 7:10 pm
Posts: 8764
Location: Buckinghamshire
Only if the answer is 42, and in the context of the Hitchhikers' Guide to the Galaxy.

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 Post subject: Re: HELPPosted: Thu Sep 05, 2013 3:55 pm

Joined: Mon Sep 10, 2012 10:51 am
Posts: 868
Found some old notes that may be of help when revising.......

Arithmetic Sequences

Example:
1, 4, 7, 10, 13, 16, 19, 22, 25, ...
This sequence has a difference of 3 between each number.
The pattern is continued by adding 3 to the last number each time.

Example:
3, 8, 13, 18, 23, 28, 33, 38, ...
This sequence has a difference of 5 between each number.
The pattern is continued by adding 5 to the last number each time.
The value added each time is called the "common difference"
What is the common difference in this example?
19, 27, 35, 43, ...

Answer: The common difference is 8
The common difference could also be negative, like this:
25, 23, 21, 19, 17, 15, ...
This common difference is -2
The pattern is continued by subtracting 2 each time.

Geometric Sequences
A Geometric Sequence is made by multiplying by some value each time.

Example:
2, 4, 8, 16, 32, 64, 128, 256, ...
This sequence has a factor of 2 between each number.
The pattern is continued by multiplying by 2 each time.

Example:
3, 9, 27, 81, 243, 729, 2187, ...
This sequence has a factor of 3 between each number.
The pattern is continued by multiplying by 3 each time.

Special Sequences

Triangular Numbers
1, 3, 6, 10, 15, 21, 28, 36, 45, ...
This Triangular Number Sequence is generated from a pattern of dots which form a triangle.
By adding another row of dots and counting all the dots we can find the next number of the sequence:

Square Numbers
1, 4, 9, 16, 25, 36, 49, 64, 81, ...
The next number is made by squaring where it is in the pattern.
The second number is 2 squared (22 or 2×2)
The seventh number is 7 squared (72 or 7×7) etc

Cube Numbers
1, 8, 27, 64, 125, 216, 343, 512, 729, ...
The next number is made by cubing where it is in the pattern.
The second number is 2 cubed (23 or 2×2×2)
The seventh number is 7 cubed (73 or 7×7×7) etc

Fibonacci Numbers
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...
The Fibonacci Sequence is found by adding the two numbers before it together.
The 2 is found by adding the two numbers before it (1+1)
The 21 is found by adding the two numbers before it (8+13)
The next number in the sequence above would be 55 (21+34)

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 Post subject: Re: HELPPosted: Thu Sep 05, 2013 4:49 pm

Joined: Tue Jul 21, 2009 9:56 pm
Posts: 8545
mystery wrote:
Could the first one have another answer of 6 x 7 as well?

Wow! Sure I had a reason then and now I have lost the meaning of life as Sally has pointed out.

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