count the balance after you pay

we entered in to a hotel nearby mathale town at the evening for a refreshment last month when travelling via that town. After we having our refreshment the bill was 680 rupees. I handed over 1000 rupee note to the waiter and I needed to get the balance quickly because we are getting too late there. So I went to the counter and got my balance. I got 220 rupees of balance instead of 320 rupees and the waiter asked "is that balance is okay".

I was shocked and tried to figure out the balance when deducting 680 from 1000. I'm sure I should get 320 rupees instead of 220 rupees and I complained it to that waiter. He went to the counter and gave me another 100 rupee note as the balance. but the waiter and the cashier didn't talked to each other. So I thought they have done the thing by planning. so, I shouted at the waiter because they given me some wrong amount of balance and trying to rob some money.

I think they do that thing to other people as wel. so, please be patient and count on your balance when you buy or pay for something at  any outlet. Some of my friends told me most of the time the cashiers do such mistakes at "bentota bake house- outlets". that robbed money goes to their pocket, not to the company drawer.