Calculating GST at 15% - Excel

If a simple gst q turns into this shit fight lets just hope we never get a trig or calculus thread q

geek_ross1970, Oct 31, 7:47 pm

Can you imagine?Biker has enough trouble understanding decimals, let alone how they relate to angles!

geek_cybertao, Oct 31, 8:35 pm


geek_greghale, Oct 31, 8:40 pm

That's the same as dividing by 720223/625000 you halfwit! LOL You just keep getting dumber!

geek_biker_69, Oct 31, 9:44 pm

In the context of percentages, such as GST, there's no such thing as 1/7th. See post #99.

There's a huge difference between knowing things you've been taught and actually understanding them... I prefer the latter.

geek_biker_69, Oct 31, 9:47 pm

I fully understand decimals and fractions. It's quite clear you're the one that doesn't.

So when are you going to post the additional calulations you have to do if you're foolish enough (as you are) to convert a given decimal for a calculation into a fraction, for absolutely no added accuracy?

geek_biker_69, Oct 31, 9:50 pm

Whoever stops posting first is correct..

geek_blenheim-trader, Oct 31, 9:53 pm

Well bugger me! Just when you think he's had enough of proving himself a fool, he goes and posts a triple whammy.

geek_cybertao, Oct 31, 9:58 pm

lets get them started on politics

geek_wotz_it_2_ya, Oct 31, 9:59 pm

If hes doesn't post again makes him the winner..

geek_blenheim-trader, Oct 31, 10:00 pm

Who would believe this thread would hit 167+

geek_blenheim-trader, Oct 31, 10:01 pm

Oh, trust me.He won't be able to help himself.It's one of his mental deficiencies.

geek_cybertao, Oct 31, 10:02 pm

Bets are on this thread hits 200 because biker69 and cybertao are too far gone down the path of making dicks out of themselves that it's too late to pull out now.

geek_ross1970, Oct 31, 10:13 pm

. Which came first the chicken or the egg.

geek_blenheim-trader, Oct 31, 10:18 pm

Where's the calcs, kocksmoker?

geek_biker_69, Oct 31, 10:20 pm

Meh, he has nothing.

geek_biker_69, Oct 31, 10:21 pm

So prove this post wrong!

100 / (720223 / 625000)= ?
100 x 625000 / 720223) = ?

What are you? A man or a moron? That's obviously rhetorical since it's clear you're a moron! Even primary school kids know that dividing by a fraction is exactly the same as multiplying by its inverse!

geek_biker_69, Oct 31, 10:26 pm

geek_blenheim-trader, Oct 31, 10:28 pm

altho to save confusion it's actually more accurate to say multiply by it's "reciprocal" instead of inverse unless you explicitly state "multiplicative inverse" seeing as how a numbers inverse isn't limited just to multiplication, whereas there is only 1 reciprocal.

Still, lets not let maths stand in the way of this epic biker/cyber dickfest.... on with the show

geek_ross1970, Oct 31, 10:39 pm

Missing the point. Any decimal or percentage can as easily be expressed (with absolute precision) as a fraction. Not all fractions can be precisely expressed as a decimal. The assertion that "fractions can be less accurate" is nonsense.

geek_little_egypt, Oct 31, 10:45 pm

No. You're missing the point. This is a thread about GST. GST is 15%. There's no need to convert to a fraction because it adds nothing to accuracy.

geek_biker_69, Oct 31, 10:54 pm

And in the examples I showed where it works for any given percentage the figures are decimals. So why would you bother to convert to a fraction?

Accuracy is only potentially lost when you're converting from a fraction to a decimal, never when converting a decimal to a fraction.

geek_biker_69, Oct 31, 10:59 pm

Had you better not quantify that by adding the word "rational" before decimal?
I'd hate someone to come back and ask you to express ( with absolute precision ) an irrational decimal ( pi perhaps? ) as a fraction.

geek_ross1970, Oct 31, 11:01 pm

I have no difficulty with it either way. Perhaps you could tutor cybertoss though. He's made an awful fool of himself with his stupid claims.

geek_biker_69, Oct 31, 11:02 pm

He's not a troll - just a fool. He'd be happy that you think him a troll though. Then he can pretend he was just pretending not to know in order to troll.

geek_biker_69, Oct 31, 11:04 pm

No. You can't have an irrational decimal.

geek_little_egypt, Oct 31, 11:11 pm

Rubbish. Express pi as a value for instance. An irrational number is an infinitley repeating decimal, and you can't express irrational numbers using intergers.

geek_ross1970, Oct 31, 11:24 pm

Pie doesn't repeat or end, and is calculated from the ratio of a circle's circumference and radius.

geek_cybertao, Oct 31, 11:33 pm

Exactly it's an irrational number. It is an infinitely repeating non-sequential decimal. As opposed to a terminating decimal eg 1/8 = 0,125, or a repeating decimal that repeats the same finite sequence eg 1/3 = 0.3333``, which are both rational numbers ( able to be created as fractions ) using integers. To say you can't have an irrational decimal is like saying you can't have our infinite number system.

geek_ross1970, Oct 31, 11:40 pm

geek_blenheim-trader, Oct 31, 11:41 pm


geek_jcmp21, Oct 31, 11:47 pm

Pi can't be represented by a decimal any more accurately than the ratio it is originally calculated from.
The ratio it is originally calculated from.

You can say pi is 3.14159265, accurate to 9 decimal places, or 62831853/20000000.Both are wrong.
You can't make a decimal that can't be a fraction.

geek_cybertao, Oct 31, 11:50 pm

Wrong. You need to bone up on what an irrational number is.

geek_ross1970, Oct 31, 11:57 pm

I know what an irrational number is; a number that can't be represented as a fraction or a decimal.

geek_cybertao, Nov 1, 12:08 am

wrong again. first bit is right if you add "using integers", second bit is wrong. Irrational numbers are infinitely repeating non-sequential decimals. eg ???2 = irrational, can't be expressed as a fraction but of course it has a decimal value that just goes on infinitely with no repeating sequence. 1.4142 bla bla bla....

Re-read the definiton more carefully, irrational numbers can't be expressed with terminating decimals or repeating decimals.

geek_ross1970, Nov 1, 12:15 am

So in other words, you can't represent an irrational number as a decimal...
Otherwise start writing down the square root of two and come get me when you are done.

geek_cybertao, Nov 1, 12:21 am

F you're dense! irrational numbers are decimal. Infinitely non-sequential. They don't terminate, they don't repeat the same sequence.

So I get back to the bit where I told little Egypt his statement in post #176 = "Any decimal or percentage can as easily be expressed (with absolute precision) as a fraction" needed to have the word "rational" added before the word decimal, otherwise it's just plain wrong unless you want to discount the basis of infinity for our entire number system.

geek_ross1970, Nov 1, 12:27 am

And I'll correct the typo: "infinitely repeating" should be "infinitley non-repeating" but it's perfectly clear from subsequent posts.

geek_ross1970, Nov 1, 12:47 am

geek_ross1970, Nov 1, 1:00 am

I was top of maths at high school in a 99% middle class white suburb. I am a girl - oh the horror!!!!!

Jumped to end of thread; did anyone mention the margin of error and rounding up/down of prices? There's no point going to 8 decimal places when dollars and cents are only 2 decimal places.

BTW I didn't do accounting so maybe there are rules when dealing with dollars and cents...

geek_ladeda, Nov 1, 7:03 am

Precisely. You CAN'T write the full and precise version of PI as a decimal, it is an infinite sequence of digits. 3.14159 is only an approximation. For any finite approximation of an irrational number such as 3.14159 it it trivially easy to express the same approximation as a fraction of exactly the same precision; in this case 314159/100000, which means the approximation of pi to any finite number of decimal places is always a rational number.

geek_little_egypt, Nov 1, 7:22 am


geek_jcmp21, Nov 1, 8:17 am

Which in no way means it's not a decimal number. There's no qualifying criteria that says a number, wether an infinite integer or irrational decimal part has to be able to be finitely written out. Our whole number system is based on infinity.

Little E, you say in #176:
"ANY decimal can be written; with absolute precision; as a fraction"

then say in #198:
"For ANY FINITE APPROXIMATION of an irrational number such as 3.14159 it it trivially easy to express the same approximation as a fraction of exactly the same precision"

Good, your second statement corrects the error in the first. "Any" and "any approximation of" aren't really the same thing aye? But like I said, add "rational decimal" to the first statement and it's correct.

then in #182 you say:
"No. You can't have an irrational decimal."

but then say in #198:
"the approximation of pi (or any other irrational number) to any finite number of decimal places...."

Which leaves the question how do you approximate, in #198, something to a finite number of decimals, when you deny in #182 that you can't have the decimal to approximate from in the first place?

geek_ross1970, Nov 1, 11:30 am

Yeah you're right, silly me. All seems to be under control ...

geek_smac, Nov 1, 11:50 am


geek_johnf_456, Nov 4, 2:31 pm

How is that a problem? You're writing a decimal approximation of the value pi (a value which cannot be written in any decimal of finite length), not a decimal approximation of the 'full decimal representation of pi'

3.141 is an approximation of pi. 22/7 is an approximation of pi. The only way to accurately express pi is by the name "pi" or the symbol "??"
You can't write or type any irrational number as a decimal because it's an infinite sequence of non-repeating digits. You also can't accurately express many fractions as a decimal in most software because they're an infinitely repeating sequence of digits and most software doesn't allow for putting a 'vinculum' over the repeating part.

geek_little_egypt, Nov 4, 2:50 pm

I guess because you are working out GST for the IRD, to be 100% accurate, you will need to use the formula they set down.

If you look at the new GST Return you will see boxe 8 say

"Multiply the amount in Box 7 by three(3) the divide the result by twenty-three (23)"

and box 12 says

"Multiply the amount in Box 11 by three(3) the divide the result by twenty-three (23)"

That is easy in excel =(a1*3/23)

I have found that when using creating a formula in excel to duplicate another system, it's often more accurate to duplicate the manual system using the same method even if it is not as pretty to look at, then you are not going to spend hours looking for a 1c balance error or similar.

geek_d.snell, Nov 5, 11:41 am

Thanks David .
Your last post was exactly what I was looking for

geek_reasonable, Nov 10, 8:40 pm

Ahhhh the mythical error when in fact the method I highlighted not only doesn't produce one but can be simply adapted to any percentage and is also instantly recognisable.

geek_biker_69, Nov 10, 9:09 pm

hi which folmula do u use to find out the gst in to the gst excl prices ? eg. $50

geek_guest, Feb 22, 6:30 pm