The average age of a teacher and three students is 20 years. If all the three students are of same age and the difference between the age of the teacher and each student is 20 years, then what is the age of the teacher?
Answer & explanation
Answer: (c) 35 years
The four ages total 80. If each student is s years old, the teacher is s + 20, so 4s + 20 = 80 gives s = 15 and the teacher is 35.
- Total of the four ages = 4 × 20 = 80.
- Let each student be s years; the teacher is s + 20.
- 3s + (s + 20) = 80, so 4s = 60 and s = 15.
- Teacher = 15 + 20 = 35 years.
- Check: (35 + 15 + 15 + 15)/4 = 80/4 = 20.
Remember · Turn an average into a total first; then express every person in one unknown.
Question and answer: UPSC's official GS Paper II (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·