If the mean and variance of five observations are and respectively and the mean of first four observations is , then the variance of the first four observations is equal to
- (A)
- (B)
- (C)✓ Correct
- (D)
Answer: (C)
Solution
Let the five observations be .
Mean of first four is , so .
Mean of all five is , so , giving .
Variance of all five: .
.
So .
Variance of the first four ... more directly:
.
Mean of first four is , so .
Mean of all five is , so , giving .
Variance of all five: .
.
So .
Variance of the first four ... more directly:
.
JEE Main · 2024 · 29 Jan 2024 · Shift 2 · Single correct option