To determine the year Sarah was born, we need to find her age in the year of her 30th birthday. We know that: Age of Sarah at 30th birthday - Age of younger sister = 5 From the information provided, we know that Sarah's younger sister couldn't attend the party because she was studying abroad, which means she is at least 18 years old (since she/she is attending a tertiary institution or similar). So, the age of Sarah's younger sister at the time of the party must be at least 18. Let's assume the younger sister's age, YS, is 18 years old. Then: YS - 5 = 18 - 5 YS - 5 = 13 YS = 18 Therefore, Sarah's age at her 30th birthday was 18 years ago. In other words, Sarah was born 18 years before 2023: Sarah's birth year = 2023 - 18 = 2005 So, Sarah was born in 2005.