Counting the change

Later that day I wanted to buy a dress for Shubhra for her birthday. The price was a hundred and seventy pesos, so I gave the lady two hundred. As she was giving me my change, I was listening to her count. After twenty-four, she said, "Thirty." I hadn't watched her, but it sounded wrong to my ear, so in front of her I started counting the change. She had only given me twenty-five pesos.