It's rare that I have come across a shop in Luxor that seems to be able to add the price of a few items up in their head quickly, most times they have to use a calculator, sometimes they have to input the prices a few times to make sure.
One example happened yesterday, I went to the local shop, I got 2 packets of Marlboro red cigarettes (16LE each) 1 litre of pepsi (5LE) and a big bag of crisps (3LE), The total price 40LE, I give the young woman 50LE, she tried adding the items up in her head and failed

I told her in Arabic it's 40LE, she went through the 4 items again, 16LE, 16LE, 5LE, 3LE and still failed to give the total price, she ended up going to the calculator and adding it up on there, she then come back with 20LE change for me, I gave her 10LE back and said you have give me too much change, she past it back to me, after a few passes back and forth she accepted I was right.
