Math problem -- help/hints please (NOW SOLVED: includes solution)

[Kevin Bewley]

Nope.. it's a fraction (I don't want to give the answer straight away here, as it's the flaw in my method I'm trying to spot) It's ONLY an A Level problem; you'd think at the age of 38 I'd find this stuff elementary. But no, I was smarter at maths when I was 18!?? :doh:

[dan sh]

The bracket you have added to 2x + 1 is not correct.

"Fear no factor", Prime Numbers.

[J4amieC]

Have you plugged 1/10 back into the original equation to check whether you're right? Thats how I always remember checking my answers during A-Level maths.

[Kevin Bewley]

Sadly not 7/11 - but you're so damn close to the real answer that you probably have done it correctly.. I'm not sure I understand the mocking Indians reference either. But no, I genuinely want to know what I'm doing wrong. I've done a whole chapter of these and got them all correct - it's just that this one is incorrect.

[Ingo]

So, if I'm not wrong: (x-4)/6 - 2x+1 = (3x-4)/2 ! -1 x/6 - 4/6 - 2x = 3x/2 - 2 - 1 ! +4/6 x/6 - 2x = 3x/2 - 3 + 4/6 x/6 - 12x/6 = 9x/6 - 18/6 + 4/6 ! -9x/6 -11x6 - 9x/6 = -14/6 ! *(-1) 20x/6 = 14/6 !*6 20x = 14 ! /20 x = 14/20 (The ! stands for the pipe followed by the operation I did in that step) Hope that is correct. :rolleyes:

------------------------------ Author of Primary ROleplaying SysTem How do I take my coffee? Black as midnight on a moonless night. War doesn't determine who's right. War determines who's left.

[dan sh]

I was wrong in my first attempt. I have changed the reply now. 7/11 is a shop supposedly, mostly run by Indians in US (I have never been to US so don't know). This is often used in stand up comic shows for jokes. That's what I was referring to.

"Fear no factor", Prime Numbers.

[Manfred Rudolf Bihy]

x-4 + 6(-2x + 1) ... etc. The error came in when you introduced the parenthesis around the second term on the left hand side. It changed the meaning of negative sign to include the one, which is not correct if you look closely at the original. Cheers!

"With sufficient thrust, pigs fly just fine."

Ross Callon, The Twelve Networking Truths, RFC1925

[dan sh]

Incorrect addition of bracket has changed the sign of 1 in the original equation which has changed your result.

"Fear no factor", Prime Numbers.

[V 0]

I came to the same solution, but filling in the actual value doesn't equal indeed. However, make sure the answer in the book is correct, because that's not always the case either. :) PS: I'm curious too now, if you find out the error, please share ?

V.

[Kevin Bewley]

Of course!! Thanks buddy! :-)

[Kevin Bewley]

Bang on (although the 'book answer' is 7/10 - simplest fractional answer). I'm curious about your notation though, what's with the factorial -1?

[Dalek Dave]

I used a different method, reducing one side to x/x = 1 and hard calculating. I got 1/10th too.

--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]

[Sumal V]

Is it just -2x + 1 ie, (-2x+1) or -(2x+1)? This makes a lot of difference...

[J4amieC]

You're slipping. I used a spreadsheet and brute forced it by checking every fraction from 0.1 to 3.0

[J4amieC]

I can tell you the answer is 7/10 but not because I can remember how to solve this from A-Level maths, but because I long ago realised such things are futile, and excel can solve this much quicker than I can.

[Ingo]

Kevin Bewley wrote:

I'm curious about your notation though, what's with the factorial -1?

Oh, that should be a pipe, but I wasn't able to type it in the editor, so it's just the remark, what I did. Forgot to post that :rolleyes:

------------------------------ Author of Primary ROleplaying SysTem How do I take my coffee? Black as midnight on a moonless night. War doesn't determine who's right. War determines who's left.

[Sumal V]

Following your same method, but only changing the brackets to 2x-1, 1(x-4) + 6(-2x+1) = 3(3x-4) multiply out the brackets: x - 4 - 12x + 6 = 9x - 12 which yields: 20x = 14 or x = 7/10

[Jonathan Nethercott]

Other people have pointed this out already (so I'm not going to take the credit for solving this), but trying to stick to your calculations as closely as possible:

(x-4)/6 - 2x+1 = (3x-4)/2

My approach was to find the lcm, which is 6 and then do this:

1(x-4) - 6(2x-1) = 3(3x-4) <-- note 2x-1, not 2x+1 because previous line is -2x + 1, not - (2x + 1)

multiply out the brackets:

x-4 - 12x+6 = 9x-12 <-- from previous line 12x+6, not 12x-6

which yields:
20x = 14
or x = 7/10

Jon CodeWrite

[Dalek Dave]

Piece of paper and a pen!

--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]

[cpkilekofp]

You dropped a sign in your third step: (x - 4) / 6 - 2x + 1 = (3x - 4) / 2 (x - 4) - 6(2x + 1) = 3(3x - 4) (x - 4) - 12x + 6 = 3(3x - 4) x - 4 - 12x + 6 = 9x - 12 -11x + 2 = 9x - 12 -20x = -14 x = 7 / 10

"Seize the day" - Horace "It's not what he doesn't know that scares me; it's what he knows for sure that just ain't so!" - Will Rogers, said by him about Herbert Hoover