to be irrationally annoyed by bad maths

[Adventurous]

So I have a piece of work I have to share with clients there are several rows of data with a cost % for each item. The total cost % is not the sum of the % over the number of rows that is just bad maths.

The cost % is the Total £ cost / Total £ revenue and breath.

Well it would mean nothing to me, I'm number dyslexic

So they think that if they pay 10% Item A and 20% Item B, the total percent cost to them for Item A + Item B is 30%??

Well done for only describing it as bad maths.

No the worked it out at 15% cost even if you bought 1 @20% and 500 @10%

Are you sure you aren't bamboozling them? It may be obvious to you what the spreadsheet or whatever it is means, but not to them perhaps.

Don't they just want to know the actual cost to them of the items? Or am I being dense, as I must admit I am not a mathematician.

change the layout or add an extra column so that it is crystal clear to someone who is really poor at maths?

Is cost % a mark-up for profit margin, or VAT or something? Very hard to picture via an internet forum, though I would probably get it eventually if I could see it and have time to study it.

Well I am not bad at maths (Got an A at A-level back in the day) but from your description I am struggling to understand what you are talking about. A worked example might help

I had one colleague who had to produce monthly graphs on call stats for an IT department (ie 50% broken hardware, 25% software upgrades, 15% password resets and 10% other)

She couldn't understand why the breakdown of call types always added up to 100% - one month she accused me of lying to her because it couldn't always be 100%!!!

I liked the manager who said they expected all departments to bring in above average figures.

I worked with a woman who didn't understand decimals at all. She thought that 0.25 was five times as much as 0.5

ok eg

A sales £100 cost £20 cost of sales 20%
B sales £1000 cost £800 cost of sales 80%

Total Sales £1100 cost £820 cost if sales (820/1100) x 100=74.5%

They had calculated (20%+80%)/2=50%

kim that is so true

kim yes listened to it on podcast today Robert Mugabe OMG

Well, I can certainly see that simply adding the two percentages together would not make sense and would not have done that.

With the way you are wording things it is perhaps a little unclear. Do you mean that item A costs £100 but is being sold at an 80% discount for £20?

Similar for item B, only using different cost and applying a different percentage figure?

Am I barking up the wrong tree (wouldn't be the first time)??

I am saying they are different products and your total cost of production is completely dependent on the number of each products (with different costs) you sell and the proportion of each product sold will affect the total production cost

If I sell loads of Product A which I make a great margin on and a few of Product B which I hardly make any money on this is fine but if its the other way round it wouldn't be.

In the calculation I was presented with the number you sold of each product was irrelevant as it was the 2 % divided by 2 which is bad maths!!

Also Kim have you listened to Freakanomics a good podcast worth a listen for a geeky mathematician (which I am not sure I am!)