Here in Hackney, East London, we regularly get offered 2 for the price of 3 - as I was last week in the local off-licence and the local news agents. "This is an offer you can
My mum bought 4 beigels for 25p each, and the girl tried to charge her Â£1.40. My mum (who used to be a programmer, and can probably add octal in her head faster than a bakery worker could count bread rolls) said "No. 4 times 25p is Â£1." The girl responded by bringing out a piece of paper and a biro and wrote on in 25p + 25p + 25p + 25p = Â£1.40 and then said "see figures can't lie!" My mum said "Ok, just give me one beigel" and handed over 25p. Then she said "OK, give me another one" another 25p handed over. Process repeated until my mum had 4 beigels and the girl had Â£1. - problem solved (and queue of potential customers dispersed).
If you are not good with mental arithmetic, don't ever buy more than one item in East London. And make sure the items scanned in the supermarket are the items that you actually take home with you. It is a regular event to buy two of something and find the till receipt mysteriously shows three of them. (and the shop WILL blame the Mysterons for it).
Tell the above to your kids and explain "that is why you have to study maths at school".
And tell the appropriate idiot at /. that Â£ is the symbol for GBP and not $AU or WTF.