Q1. [1]
The mean of five observations is 15. If the mean of first three observations is 14 and that of the last three observations is 17, then the third observation is
- A $20$
- B $19$
- C $18$
- D $17$
Previously asked in CBSE board exam
2024 30/3/1 Q16
Generated by claude-sonnet-4-6 · 2026-06-15 10:33 · grounding rag
Model Answer
Option (A) 20
Sum of 5 observations = 15 × 5 = 75; Sum of first 3 = 14 × 3 = 42; Sum of last 3 = 17 × 3 = 51.
Third observation = 42 + 51 − 75 = 20.
Explanation
The third observation is counted in both "first three" and "last three" groups. So: 3rd obs = (Sum of first 3) + (Sum of last 3) − (Total sum) = 42 + 51 − 75 = 20. This is a standard trick question on means.
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