You may have noticed the sound “yāo” in the very beginning. What is “yāo”? You’ve already known “yī” for the number “one”. When saying a series of numbers digit by digit, such as a telephone number, hotel room number, order number, receipt number, etc., many people in mainland China would say “yāo” for the digit “one”. So if a number is involved in your conversation and you hear people say “yāo”, don’t be surprised.