Q1. [1] § 13.2 Mean of Grouped Data
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.
If a question refers to an image, map, graph or diagram that is not shown here, find the actual CBSE question paper on the CBSE website:
cbse.gov.in.