Not near as scary as any time a cashier in one of the local supermarkets is called upon to do basic arithmetic:

Recent in the expensive supermarket, where the cashiers SEEM to be well educated: I was purchasing only four identical items at $1.99 each. The total came to $9.95. So I said "That's not correct. You must have keyed in one too many". He said "No. Four bags at 1.99. The total is 9.95". I said "1.99 is a cent less than two dollars, so four of them is four cents less than eight dollars". I might as well have been talking Greek. He had no clue what I meant. Eventually I got him to advance the tape and see that it showed one at 1.99 followed by four at 1.99. That he understood and knew how to correct.

Yesterday in the market where the cashiers are definitely not educated: The total was $59.20. I handed her three twenties and two dimes. She keyed in something (obviously just $60) and the register said the chance was $.80. So she pulls out 80 cents and starts to hand it to me. I said "No. I gave you $60.20". She said "Yes?" I said "so the change should be a dollar". She said "No. It's 80 cents". I said "The total was 59.20". She looked at the register and said "yes". I said "and I gave you 60.20". She was totally confused and flustered at that point. She said "What should the change be?". I said "one dollar" and she handed that to me.