Sarah was born in 1993. Let's break this down step-by-step: 1. We know that Sarah celebrated her 30th birthday in 2023. 2. Her younger sister is 5 years younger than her and couldn't attend the party because of studying abroad. 3. If Sarah is 30 in 2023, then her sister would be 25 that same year. 4. The difference in age between them is 5 years. 5. Therefore, if Sarah was born in 1993 and her sister was born 5 years later, her sister would have been born in 1998. 6. The only possible year for Sarah's birth based on this information is 1993. Sarah was indeed born in 1993. She turned 30 in 2023, which matches the information provided about her age and her sister's age difference and study abroad situation.<|end_header_id|>