Question

The mean of $25$ observations is $36$. Out of these observations if the mean of first $13$ observations is $32$ and that of the last $13$ observations is $40$, the $13$th observation is :

• A. $23$
• B. $36$
• C. $38$
• D. $40$

Answer 1

Answer: (B)

$36$

Mean of $25$ observations =$36$
Sum of $25$ observations = $36\times 25=900$
Mean of first $13$ observations= $32$
Sum of first $13$ observations = $32\times 13=416$
Mean of Last $13$ observation=$40$
Sum of Last 13 observations = $40\times 13$ = $520$
Sum of first$13$ observation+ Sum of last$13$ obs $-$ $13$th observation$=$ Total sum of $25$ observations
$416+520-13thobservation=900$

• $13$ th observation $=36$