Puzzle

[Judd]

6 6 8 12 12 24 20 xx 36


What is xx and why?

[sql_lall]

The thread title should be "puzzles", not just puzzle
Because, this is another case of two series in one:
Splitting every second number into another series you get:
6 8 12 20 36... and
6 12 24 xx...

Now, the top series is: a_n=4+2ⁿ
Bottom series is a_n=6*2^n-1
=> bottom series continues 6 12 24 48

=> xx=48

series to more terms is:
6 8 12 20 36 68 132... +
6 12 24 48 96 192 384...=

6 6 8 12 12 24 20 48 36 96 68 192 132 384...

[Judd]

I knew it was in there somewhere!

My sister is looking for a new job and has bought a 'how to pass basic numeracy tests' book. She tried to do this one and couldn't figure it out, neither could I

[Darkwraith]

IDK. Maybe I am stating the obvious, but is it 20 and each of the x's represents a digit? My reasoning for this is that you have 2 of one number and one of the next.

6 6 8 12 12 24 20 xx 36

[Judd]

Well the answer in the book was 48....I knew the answer, but not the reason...

[Darkwraith]

oh well. i think that 20 would work if the pattern kept on repeating 2 of the first and 1 of the second.

[twanvl]

The answer could also be 49.75:
f(1) = 6
f(2) = 6
f(3) = 8
f(4) = 12
f(5) = 12
f(6) = 24
f(7) = 20
f(9) = 36

An axample of such a function is:
f(x) = .0361607142*x⁷ - 1.14305555*x⁶ + 14.61875*x⁵ - 97.4722222*x⁴ +363.0635416*x³ - 747.134722*x² + 776.2815476*x - 302.25

[alkatran]

The answer is 529.

Go on, proove me wrong

If I made an Xth degree equation it IS possible.

[sql_lall]

Yeah, yeah, with a polynomial of anything above degree 7, many answers can be found.
However, i think because it is a sample question from a *Basic* numeracy test, i am guessing that you aren't expected to generate such polynomials in your head.

However, in all fairness, 529 is a perfectly reasonable answer.
If you make f(8) anything you want, as you then have x and y values for 9 points, you can then use Lagrange Interpolation

http://mathworld.wolfram.com/Lagrang...olynomial.html

(which i must admit is a very cool and simple idea) to come up with an appropriate polynomial to show ur answer is correct

hope this helps, that really whatever ur answer is, its correct so long as you can show why.