Consider the following sum:
• + 1• + 2• + •3 + •1 = 21•
In the above sum, • stands for
Answer & explanation
Answer: (d) 8
Treat • as one digit x and write every term by place value. The equation 23x + 34 = 210 + x gives x = 8.
- Let • = x. Then 1• = 10 + x, 2• = 20 + x, •3 = 10x + 3, •1 = 10x + 1 and 21• = 210 + x.
- Left side: x + (10 + x) + (20 + x) + (10x + 3) + (10x + 1) = 23x + 34.
- 23x + 34 = 210 + x, so 22x = 176 and x = 8.
- Check: 8 + 18 + 28 + 83 + 81 = 218, which is 21• with • = 8.
Remember · Write each symbol-number by place value (tens digit × 10 + units digit), then solve one linear equation.
Question and answer: UPSC's official GS Paper II (2018, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·