Consider the following pattern of numbers:
| 8 | 10 | 15 | 13 |
| 6 | 5 | 7 | 4 |
| 4 | 6 | 8 | 8 |
| 6 | 11 | 16 | ? |
What is the number at? in the above pattern?
Answer & explanation
Answer: (a) 17
In each column the result is the first number plus the third minus the second: 8 + 4 − 6 = 6, 10 + 6 − 5 = 11 and 15 + 8 − 7 = 16. The last column gives 13 + 8 − 4 = 17.
- Column 1: 8 + 4 − 6 = 6. Column 2: 10 + 6 − 5 = 11. Column 3: 15 + 8 − 7 = 16.
- The same rule — top + bottom − middle — fits all three complete columns.
- Column 4: 13 + 8 − 4 = 17.
Remember · In column puzzles, try simple combinations (+, −, ×) of the entries on every complete column before filling the gap.
Question and answer: UPSC's official GS Paper II (2018, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). ·