Mental Arithmetic Pays, Literally

You can barely see a newspaper these days without having your mental arithmetic skills challenged.  Under the guise of a ‘mental gym’ a ‘maths challenge’ or similar, we are presented with a series of sums to perform.

Depending on your choice of newspaper, these can be fairly easy or almost impossible to really do in your head.  However, there are occasions where maths pays, or at least being able to approximate totals.

At the supermarket today I bought six things, and the bill seemed too high at £15.49 for them.  On leaving the supermarket I double checked and realised it was £2.88 too high as they had charged twice for a battery, when I had only bought one.

So mental arithmetic, or at least approximating what the total would be in my head, saved me £2.88.  Here are the prices of what I actually bought - what would your approximation of the total of these be as you were going around?

Magazine: £3.25; Battery: £2.88, Greeting card: £1.49, Chocolates: £3.66, Pastry: £0.89, Paper: £0.60