TV3 Mathematics Failure

, posted: 21-Sep-2010 18:24

In a story about Labour spinning the GST rise with dodgy figures, TV3 isn't doing much better, break out your calculator on the "National" numbers below, (the 189.34 is GST ex).


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Comment by tristanb, on 21-Sep-2010 18:42

I saw TV3's story and cringed too. Everyone knows that if you are insulting someone's maths/spelling/grammar, you better make sure that yours is perfect.

I think we need a campaign educating people that prices should increase by only 2.2%. Otherwise we are going to be gouged by retailers wanting more money.

TV3 should pay for this campaign, as part of their apology.

Comment by hellonearthisman, on 21-Sep-2010 19:16

I don't have a calculator, can you show the maths for me?

Comment by sbiddle, on 21-Sep-2010 19:21


GST is increasing by 2.5% from 12.5% to 15%  - TV3 didn't get this wrong. It does only represent a 2.2 increase on top of the 12.5% if you are adding it however, but this isn't what TV3 have done.

Their fail was that $189.34 + 12.5% is not $212

TV3 got it wrong last time as well

Author's note by sleemanj, on 21-Sep-2010 20:36


They calculated the 12.5% wrong (short $1)
  189.34 * 1.125 = 213.0075

They calculated 2.5% wrong (extra $1)
  189.34 * 0.025 = 4.7335


Comment by tristanb, on 21-Sep-2010 22:19

Well, I guess I proved my first point! :-D

Although, to be fair I never stated what TV3 did. I just brought up the fact that the number people need to think about is 2.2% when they're looking at prices next month. Prices are what is important to people shopping, not nett gain in tax. Their $100 shopping bill will soon be $102.20.

BTW I'm not a mathematician, but isn't the rate of GST going up by 20%?
2.5 is 20% of 12.5.
Maybe Labour should have tried this.

Comment by Linuxluver, on 21-Sep-2010 22:24

Duncan Garner isn't a good political journo. 

I don't watch him if his face appears. Whatever he says will almost certainly be incomplete, misleading or wrong....or some combination of all three.  

Comment by wreck90, on 22-Sep-2010 06:39

what'ya expect, brain drain and all. 

All the journos with decent maths are overseas.

Comment by 1080p, on 22-Sep-2010 07:41

TV3 had the working wrong, but the end answer correct.

Had it been the other way around they would have been praised by our education system.

The mind boggles.

Comment by robbyp, on 23-Sep-2010 13:55

Wasn't 12.5% of the gst introduced by labour, and just 2.5% introduced by national. Pehaps natioanl should rebut with that fact. The whole 15% isn't of nationals doing, so it isn't Nationals 15% GST rise. It is a case of very confusing  advertising, and doesn't look good for labour, if they do that sort of thing all the time to advertise facts to NZers

Comment by paragonOfGeek, on 23-Sep-2010 15:22

end answer is not correct.

189.34 + 12.5% = 213.0075 + 2.5% = 218.332688 =/= 217.74

189.34 + 15% = 217.74

The IRD also has this obsession with whole numbers. They cannot tell someone to calculate the new price of something by simpilly saying 
old price X (115/112.5) = new price....nooo they have to have it has to be the less understandable (46/45) where is the relevance to the actual percentages involved....sure gives the same answer but does not help people understand where these numbers are coming from

Author's note by sleemanj, on 23-Sep-2010 16:28


Yes, labour introduced 10% GST then it was increased to 12.5%.

To be fair though, it was quite a different Labour  than we have now, Roger Douglas (who was the labour finance minister behind the introduction) and his chief cohort Richard Prebble were not exactly a bastion of left wing politics, or even very centrist!


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James Sleeman
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