Correct option is A
Given:
The mean of 21 observations is 42.
The mean of the first 11 observations is 50 .
The mean of the last 11 observations is 35.
Formula Used:
Mean =
Solution:
Total of 21 observation = 42 × 21= 882
Total of 1st 11 observation = 11 × 50= 550
Total of last 11 observation = 11 × 35=385
Total of first and last 11 observation =550+385 935
So, 11th observation = 935 - 882= 53