At the supermarket the elderly lady needed to pay one dollar at the counter. She made a mistake and mistook a hundred-dollar bill for a ten-dollar bill and gave the hundred-dollar bill to the cashier. The cashier returned nine dollars to her. The cashier ripped her off for ninety dollars!
 make a mistake mistake something for somethingmake a mistake 通常就能用來表示糊里糊塗，而 mistake A for B 指把 A 誤認為 B 的意思。