Here’s a little test of your observation skills: how much would you expect to pay for one of the bottles of tea-tree oil pictured?
If you said £3.09, you’re wrong. If you said £4.09, I can see that you’ve worked out this is a trick question, but you’re also wrong.
Don’t worry, I got it wrong too. I bought one of the bottles of tea-tree oil from that shelf and I didn’t realise until I left the shop that I’d been charged £7.79 for it.